Wednesday, April 26, 2017

2-position of LSD

The carbon skeleton of indole is represented by a pentagon and hexagon fused together. The nitrogen, on the pentagon section, is the only nitrogen in the molecule. Typical naming in organic chemistry treats this nitrogen as number 1, thus the 2-position of indole refers to the second atom from it. If indole or 5-HT is superimposed on the LSD molecule, its 2-position is analogous to the 2-position of LSD, making it easy to compare the three molecules.

The 2-position of LSD has the highest free valence, suggesting that this site may be involved in electron donation in charge-transfer complexes (Kier, 1971). Likewise, the 2-position of 5-HT has been identified as having a high frontier electron density. In discussions of HOMO and LUMO values of different molecules, Snyder wrote,
"As with all the tryptamine derivatives examined, the region of the highest frontier electron density in LSD is at the #2 carbon atom." (Snyder,S.H. 1965)
In the formation of a charge-transfer complex, electron acceptor molecules interact with specific sites of the indole ring, rather than with the pi electron system as a whole. For example in the formation of serotonin-picrate crystals, the nitro groups of picric acid were found to interact with C-2 and C-3 of 5-HT (Bugg and Thewalt, 1970). Thus, there are some striking features about Carbon-2 and Carbon-3 whether in 5-HT or LSD.

Snyder continued,
"If a charge transfer mechanism is involved in the hallucinogenic action of LSD, the #2 carbon should be critical for this activity. It is, therefore, interesting to note that 2-Brom-LSD and 2-oxy-LSD, which contain sterically obstructing substituents at the #2 carbon, are devoid of hallucinogenic effect, even though they readily enter the brain." (Snyder,S.H. 1965)
According to Snyder, the reason for greatly diminished or no psychelic effects in the 2-brom derivative of LSD (BOL-148) is because the bromine atom obstructs the reactive site. Alternately, a bromine at position-2 could alter the electronic properties of the molecule as a whole, so that it is less likely to interact with the biological receptor. In terms of its outer shell configuration, bromine brings at least 3 sets of paired electrons in its p-orbitals. Adding these sets of paired electrons could weaken the pi cloud.  A similar situation may happen with oxygen in 2-oxy-LSD although it has 2 sets of paired electrons. 

It has been noted that lifting the 2,3-double bond in LSD weakens drug potency considerably (Keup, 1970). This would suggest that a change in the electronic properties, and not necessarily steric bulk, is what accounts for diminished potency of BOL-148.

MLD-41 differs from LSD by 1 methyl group on Nitrogen 1. It is just 10X less potent than LSD, so it is not like BOL-148 which is much less potent or 2-oxy-LSD which is said to be biologically inactive. The Carbon in the methyl group would have no pairs of electrons in its outer shells; its outer shell electrons are involved with C-C and C-H bonding. Could it affect the nearby pi clouds? The methyl group on the Nitrogen is small, so it seems unlikely that steric bulk would keep it from interfacing well with the receptor. 

It has also been reported, by Kumbar and Sankar, that there is a significant frontier electron density present on carbon 8 of LSD (Kumbar and Sankar, 1973).


Reference

Snyder S. H. and C. R. Merril (1965). A relationship between the hallucinogenic activity of drugs and their electronic configuration. Proceedings of the Natational Academy of Sciences U. S. A. 54, 258-266.


Bugg C. E. and U. Thewalt (1970). Crystal structure of serotonin picrate, a donor-acceptor complex. Science 170, 852-854.

Keup W. 1970. Structure-activity relationship among hallucinogenic agents; In Origin and mechanisms of hallucinations. Proceedings of the 14th annual meeting of the Eastern Psychiatric Research Association held in New York City, November 14-15, 1969, W. Keup (Ed.), Plenum Press, New York, pp. 345-376.

Kier L. B. Molecular orbital theory in drug research. New York, Academic Press, 1971.

Kumbar M. and D. V. Sankar (1973). Quantum chemical studies on drug actions. 3. correlation of hallucinogenic and anti-serotonin activity of lysergic acid derivatives with quantum chemical data. Research communications in chemical pathology and pharmacology 6, 65-100.

Thursday, April 20, 2017

BOL-148

BOL-148 is the 2-brom derivative of LSD. There is a Bromine (Br) in place of Hydrogen at position 2.


In spite of its close structural relationship to LSD, BOL-148 has no psychedelic effects. Among the LSD analogs, BOL-148 is especially important because it indicates that substitution at the 2-position can change the activity of the whole molecule, as outlined by the studies below.

In 15 healthy males, doses of 75-110 ug/kg BOL-148, which 100X exceed an effective dose of LSD, caused no change in pupillary dilation, patellar reflex, or blood pressure (Isbell et al., 1959). BOL-148 did not alter the behavior of 6 individuals with schizophrenia, when given at 10X the dosage of active LSD, although for BOL-148 these doses may have been too low to observe any effect. BOL-148 1 mg twice a day for 2 weeks, or 5 mg for 3 days had no evident effect on their psychoses (Turner and Merlis, 1958).

There is evidence of the contrasting pharmacological effects of LSD and BOL-148 on the EEG. While LSD affects the EEG in doses of 100 ug/kg, BOL-148 in doses of 100+ ug/kg are reported to be without effect on the EEG, and generally when there is no EEG effect, no drug effect is expected. BOL-148 did not cause any sign of the fast electrical activity or alerting behavior seen with injections of LSD in cats, even when doses of up to 100 ug/kg of BOL-148 were used intraventricular, to avoid the blood-brain barrier (Bradley and Hance, 1956). BOL-148 is reported to produce no EEG changes in Macaca mulatta, in high dose ranges 110-175 ug/kg (Monroe and Heath, 1961). Saline gave the same response as 1000 ug/kg BOL-148 in cats with permanently implanted EEG electrodes (Eidelberg et al., 1965). In rabbits, 500 ug/kg BOL-148 failed to produce EEG alerting for longer than 15 minutes (Schweigerdt et al., 1966). These studies indicate a lack of effect of BOL-148 on the EEG across a range of species.

BOL-148 has a very slight change in molecular structure compared to LSD, but it has none of the behavioral effects of LSD. LSD causes behavioral arousal in cats whereas BOL-148 produces mild sedation, when the two drugs are administered intraventricularly (Bradley and Hance, 1956). In rabbits, LSD enhances eyeblink conditionining, whereas BOL-148 has a neutral effect (Harvey, 2003). No affective changes in Papio papio are observed after BOL-148 in doses of 2-4 mg/kg (Fairchild et al., 1980).

Table 3 below shows the questionnaire responses for LSD and several LSD derivatives. LSD is the most potent drug, and caused the most positive responses on the questionnaire. BOL-148 is on this table, and there were few positive responses on the questionnaire at doses of 80 ug/kg, or 50 times the active dose LSD. This shows a lack of effect of BOL-148 as reported by human volunteers.


There is some evidence that BOL-148 pre-treatment protects against LSD psychosis. Studies in rabbit have shown that BOL-148 1 mg/kg had no direct temperature effect, as LSD does, but prevented the pyretogenic actions of LSD (Horita and Gogerty, 1958). In humans, BOL-148 did not function as a direct LSD antagonist since intravenous injections of BOL-148 at the height of a LSD trip did not cancel the LSD effects, but pre-treatment with BOL-148 in nonpsychotic humans did produce tolerance to the LSD reaction.

In an experiment with 10 men, pretreatment with BOL-148 for 5 days (1 mg BOL-148 three times daily) significantly attenuated LSD 0.5-1.5 ug/kg psychosis. As shown in Table 3 (below), blood pressure, pupil size and number of positive responses to questionnaire were reduced during LSD challenge 5 days after BOL-148 pretreatment (Isbell et al., 1959). The tolerance-producing effect of BOL-148 does suggest that it may act on similar pathways as LSD.


Some assays have indicated similarities between LSD and BOL-148. For example, LSD and BOL-148 were found to have the same affinity for beta-adrenergic receptors (Dolphin et al., 1978), and were equally effective as MAO and acetylcholinesterase inhibitors in histochemical analysis of rat brain (Shanthaveerappa et al., 1963). However it is important to keep in mind that these samples did not involve the whole organism.

There is one report from 1957 indicating that BOL-148 may function as a hallucinogen in high doses. Two normal volunteers experienced psychic effects when BOL-148 was administered intravenously to total doses of 18 and 22 mg, or equivalent to ~200 LSD doses.
"In man small doses of bromo-LSD are said to produce none of the bizarre psychic effects noted with LSD but this is not the case when bromo-LSD is administered intravenously in large doses. Thus, when constant intravenous infusions of bromo-LSD were given to normal subjects, both experienced psychic changes, which became more severe as the infusion continued and persisted for 3 to 4 hours after the infusion was stopped. No hallucinations were noted but there were feelings initially of drowsiness, depression, anxiety, and apprehension followed by feelings of irritation, restlessness, and tenseness, and later, intensely disagreeable sensations of unreality and depersonalization, inexplicable feelings of strangeness and mild confusion." (Schneckloth,R. 1957)
A relatively large body of work exists on human studies with BOL-148, making it one of the most well characterized LSD analogs. BOL-148 shows that structure-activity relationships can be quite revealing about the mechanism of action of LSD, since substitution at the 2-position can change the activity of the whole molecule. Another important research finding related to BOL-148 research is that LSD does not induce a psychosis by creating a relative deficiency of 5-HT within the brain. BOL-148 has been shown to have more anti-5-HT activity than LSD in vitro and in vivo, thus if LSD worked by blocking 5-HT neurotransmission, BOL-148 would be expected to be a more potent hallucinogenic drug, but BOL-148 is inactive on many accounts.


Reference

BRADLEY P. B. and A. J. HANCE (1956). The effects of intraventricular injection of d-lysergic acid diethylamide (LSD 25) and 5-hydroxytryptamine (serotonin) on the electrical activity of the brain of the conscious cat. The Journal of Physiology 132, 50-1P.

Dolphin A., A. Enjalbert, J. P. Tassin, M. Lucas and J. Bockaert (1978). Direct interaction of LSD with central "beta"-adrenergic receptors. Life Sciences 22, 345-352.

Eidelberg E., M. Long and M. K. Miller (1965). Spectrum analysis of EEG changes induced by psychotomimetic agents. International Journal of Neuropharmacology 4, 255-264.

Fairchild M. D., D. J. Jenden, M. R. Mickey and C. Yale (1980). EEG effects of hallucinogens and cannabinoids using sleep-waking behavior as baseline. Pharmacology, Biochemistry, and Behavior 12, 99-105.

Harvey J. A. (2003). Role of the serotonin 5-HT(2A) receptor in learning. Learning & Memory 10, 355-362.

HORITA A. and J. H. GOGERTY (1958). The pyretogenic effect of 5-hydroxytryptophan and its comparison with that of LSD. The Journal of Pharmacology and Experimental Therapeutics 122, 195-200.

ISBELL H., E. J. MINER and C. R. LOGAN (1959). Relationships of psychotomimetic to anti-serotonin potencies of congeners of lysergic acid diethylamide (LSD-25). Psychopharmacologia 1, 20-28.

ISBELL H., E. J. MINER and C. R. LOGAN (1959). Cross tolerance between D-2-brom-lysergic acid diethylamide (BOL-148) and the D-diethylamide of lysergic acid (LSD-25). Psychopharmacologia 1, 109-116.

MONROE R. R. and R. G. HEATH (1961). Effects of lysergic acid and various derivatives on depth and cortical electrograms. Journal of Neuropsychiatry 3, 75-82.

SCHNECKLOTH R., I. H. PAGE, F. DEL GRECO and A. C. CORCORAN (1957). Effects of serotonin antagonists in normal subjects and patients with carcinoid tumors. Circulation 16, 523-532.

Schweigerdt A. K., A. H. Stewart and H. E. Himwich (1966). An electrographic study of d-lysergic acid diethylamide and nine congeners. The Journal of Pharmacology and Experimental Therapeutics 151, 353-359.

SHANTHAVEERAPPA, T. R., K. NANDY and G.H. BOURNE (1963). Histochemical studies on the mechanism of action of the hallucinogens D-lysergic acid diethylamide tartrate (lsd-25) and D-2-bromo-lysergic acid tartrate (bol-148) in rat brain. Acta neuropathologica 3, 29-39.

TURNER W. J. and S. MERLIS (1958). Chemotherapeutic trials in psychosis. III. 2-Brom-d-lysergic acid diethylamide (BOL 148). The American Journal of Psychiatry 114, 751-752.

Serotonin-binding protein and LSD

Serotonin-binding protein

A ~50 kDa protein that binds serotonin was first identified in 1974. It was discovered by passing all of the soluble extracts of a cell over a 5-HT affinity column, and then eluting the column with 5-HT. The protein was stored with 5-HT to prevent degradation.

Serotonin-binding protein is expressed in enteric and central serotonergic neurons, including enterochromaffin cells, the nuclei raphe dorsalis, centralis superior, raphe medianus, raphe magnus, raphe obscurus, and raphe pallidus. Also, dense staining with antibodies to serotonin-binding protein was found in the supraependymal plexus lining the ventricular surfaces.

Serotonin-binding protein and LSD

In 1977, Shih and colleagues performed spectroscopic analysis of free LSD and LSD bound to serotonin-binding protein. Free LSD exhibited max fluorescence at 435 nm with excitation at 330 nm, while serotonin-binding-protein-bound-LSD shifted its fluorescence and excitation maximum to 465 nm and 375 nm. These results suggest that the interaction between LSD and serotonin-binding-protein caused a delocalization of the molecular orbital electrons and thereby lengthened the electronic conjugation of the drug molecule.

Figure 2 below shows the excitation (330 nm) and emission (435 nm) wavelengths of free LSD.


Figure 3 shows the excitation (375 nm) and emission (465 nm) wavelengths for protein-bound-LSD.


An increase in the absorption and emission wavelengths was also observed when bovine serum albumin (BSA) was mixed with LSD, as shown in the next figure. Peak 1 is the fluorescence of BSA. Peak 2 is shifted towards longer wavelengths, and represents the BSA-LSD complex.


Generally, a shift of the absorbance towards longer wavelengths can be accomplished by adding Sulfur, Nitrogen, or Oxygen to a molecule, which increases the number of loosely bound electrons. Serotonin-binding-protein and other proteins contain lone pairs of electrons from S, N, and O that can add to the pi-electron system of the LSD molecule, thus modifying its spectra absorbance.


Reference

Shih J. C. and J. Rho (1977). The specific interaction between LSD and serotonin-binding protein. Research communications in chemical pathology and pharmacology 16, 637-647.

Wednesday, April 19, 2017

Beta2-Adrenergic receptor crystal structure

Good news from The Scripps Research Institute. The human beta2-adrenergic receptor (beta2-AR) has been crystallized ! !



Hallucinogenic molecules bind to G-protein coupled receptors (GPCRs), a large family that includes the beta2-AR and serotonin 2A receptor (5-HT2AR). A popular theory is that hallucinogens such as psilocybin and DMT affect constitutive signaling at the 5-HT2AR. Hallucinogenic drugs probably bind to dopamine GPCRs too. The results with the carazolol-bound beta2-AR structure can be extended to psychedelic research since the 5-HT2AR is highly conserved with the beta2-AR, and the beta2-AR was crystallized with the inverse agonist carazolol, which closely resembles psilocin.



Figure 5 below shows carazolol (yellow) bound to the beta2-AR.


The beta2-AR has seven transmembrane helices (Figure 1 below). Intracellular loop 3 (ICL3) is found on the intracellular side of the cell membrane, where G-proteins bind to the receptor. The 5-HT2AR couples to Gq/11, via interactions involving ICL3. The ICL3 domains of various GPCRs have been shown to provide docking sites for beta/gamma G-proteins subunits, as well as arrestins.


GPCRs have amazing structural plasticity to accommodate many different binding ligands. In particular, the ICL3 has been identified as a highly unstructured region using protease susceptibility and intramolecular fluorescence resonance energy transfer experiments. Obtaining high-resolution structures of GPCRs has been challenging because of the unstructured regions. The inherent flexibility of the ICL3 region probably leads to the receptor's conformational heterogeneity and crystallization problems.

The authors developed a strategy to obtain the beta2-AR crystals. They replaced ICL3 with T4 lysozyme (T4L), a well-folded protein that restricts the movement of helices. The final construct used for crystallization trials had residues 231 to 262 of the beta2-AR replaced by amino acids 2 to 161 of T4L. The authors called the fusion protein "beta2-adrenergic receptor-T4L," or beta2-AR-T4L.


The beta2-AR-T4L did not couple to G-proteins, so it was not a functional receptor, and the presence of T4L at the ICL3 region could potentially affect the arrangement of the normal protein, but there didn't seem to be another option. The researchers set up over 2,000 conditions at 4 C and 20 C to attempt to grow wild-type crystals of beta2-AR.
"Despite substantial efforts, we were unable to grow diffraction-quality crystals from purified, homogeneous wild-type (WT) beta2-adrenergic receptor." (Rosenbaum,D.M. 2007)
This effort is a testimony to the flexibility of the beta2-AR and perhaps GPCRs in general. A tightly packed protein such as T4 lysozyme can be crystallized easily, but a native GPCR cannot be crystallized because it vibrates too much to "freeze out". By attaching T4L as a seed for the crystallization process, the researchers sufficiently minimized the molecular motions of the beta2-AR protein.

Another strategy for obtaining beta2-AR crystals involved making monoclonal antibodies to the ICL3, and then fragments of these antibodies (Fab). The researchers were able to crystallize a beta2-AR-Fab5 construct, and remarkably, binding of Fab5 to beta2-AR did not alter agonist or antagonist binding affinities, so presumably the native structure of the beta2-AR was unaffected.

The figure below shows the constructs that were crystallized: beta2-AR-T4L (blue/grey) and the beta2-AR-Fab5 (yellow/grey).


In the previous 7 years, rhodopsin was the only GPCR structure that was available. It was possible to infer structure-function relationships in GPCRs by referring to rhodopsin, but in the next few months, the beta2-AR crystal structure may be utilized to generate better theoretical models of the 5-HT2AR, which has not yet been crystallized, and make predictions about the orientation of hallucinogens in the binding pocket. The beta2-AR crystal structure may be utilized in the next months to generate better theoretical models of the 5-HT2AR, which has not yet been crystallized, and make predictions about the orientation of hallucinogens in the binding pocket.


Reference

Cherezov V., D. M. Rosenbaum, M. A. Hanson, S. G. Rasmussen, F. S. Thian, T. S. Kobilka, H. J. Choi, P. Kuhn, W. I. Weis, B. K. Kobilka and R. C. Stevens (2007). High-resolution crystal structure of an engineered human beta2-adrenergic G protein-coupled receptor. Science 318, 1258-1265. 10.1126/science.1150577

Rosenbaum D. M., V. Cherezov, M. A. Hanson, S. G. Rasmussen, F. S. Thian, T. S. Kobilka, H. J. Choi, X. J. Yao, W. I. Weis, R. C. Stevens and B. K. Kobilka (2007). GPCR engineering yields high-resolution structural insights into beta2-adrenergic receptor function. Science 318, 1266-1273. 10.1126/science.1150609

Rasmussen S. G., H. J. Choi, D. M. Rosenbaum, T. S. Kobilka, F. S. Thian, P. C. Edwards, M. Burghammer, V. R. Ratnala, R. Sanishvili, R. F. Fischetti, G. F. Schertler, W. I. Weis and B. K. Kobilka (2007). Crystal structure of the human beta2 adrenergic G-protein-coupled receptor. Nature 450, 383-387. 10.1038/nature06325



Tuesday, April 18, 2017

Abramson's Cold Spring Harbor Questionnaire for human LSD research

“One of the serious objections to questionnaires is that the validity of individual items is doubtful. Nevertheless, there are many items whose validity cannot be pushed further than a subjective response. Unfortunately, the only way to tell whether a person has hallucinations, or a headache, for that matter, is to ask him. As our science progresses, more objective tests for these phenomena may be evolved. In the meantime, it would seem that the proper course for the scientific psychologist to follow lies somewhere between complete dependence upon verbal reports of individuals and complete rejection of such material." (Jarvik,M.E. 1955)

Many of the workers who have studied mescaline or LSD intoxication have been puzzled by the subjects' attitudes. Efforts of the investigator to involve the subject in organized activities, such as answering questions, may be answered with reluctance or frank refusal.

Even though the questionnaire technique is not always reliable, it has been valuable in connection with psychoactive drug research to assess the relative potency of LSD and LSD congeners in humans. The most common questionnaire is the Cold Spring Harbor Questionnaire, shown below.


The 59-item questionnaire has short questions like, "Do you feel unsteady?" and "Are you anxious?" In 1955, Jarvik and Abramson found that LSD led to a large number of positive responses on the Cold Spring Harbor Questionnaire, and far more positive responses than the drugs LAE-32, BOL-148, ergonovine, scopolamine, alcohol, methamphetamine (methedrine), and two placebos. The subjects were 5 nonpsychotic volunteers, who received all drugs on different occasions.

Questionnaires and physiological tests were administered during the drug effects. As shown in the results below, LSD produced the most positive responses of all the drugs tested, thus validating the usefulness of the Cold Spring Harbor questionnaire for LSD research.


“In comparing the effects of seven different chemical and two tap water placebos upon the responses to a questionnaire, it is apparent that the chemical structure of the compound ingested is of paramount importance in determining responses to these questionnaires.” (Jarvik,M.E. 1955)

An abbreviated version of the questionnaire with 47 items was used with much of Abramson's human LSD research. The Table below gives the questions and responses by 26 volunteers, at 0.5 h, 1.5 h, 2.5 h, and 3.5 h after LSD ingestion. The questions that frequently gave a "yes" answer were, "Is salivation increased?", "Do you have a funny taste in your mouth?", "Is it a bitter taste?", "Does your head ache?", "Do your hands and feet feel peculiar?", "Is there pressure in your ears?", "Is your hearing abnormal?", "Do you tremble inside?", and "Are you anxious?"


The test situation in which a subject is asked to respond to these questions has turned out to be relevant for assessing some commonalities of the LSD experience.


Reference

JARVIK M. E., H. A. ABRAMSON and M. W. HIRSCH (1955). Comparative subjective effects of seven drugs including lysergic acid diethylamide (LSD-25). Journal of Abnormal Psychology 51, 657-662. 10.1037/h0041073

Abramson H. A., M. E. Jarvik, M. R. Kaufman, C. Kornetsky, A. Levine and M. Wagner (1955). Lysergic acid diethylamide (LSD-25): I. physiological and perceptual responses. Journal of Psychology 39, 3-60.

Monday, April 17, 2017

Serotonin pain

Pain researchers devised a method for assessing human pain. A blister was induced to the same part of the hand of each subject, and the blister base was used as the testing ground for certain drugs. When serotonin was applied to a blister base, there was a 19 s delay between the time of 5-HT administration and the perception of pain as reported by human volunteers. The figure below is a graphic representation of the pain caused, with pain on the y-axis. Higher concentrations of 5-HT caused more intense pain. This experiment verified the hypothesis that the pain of a wasp sting may be related to the 5-HT content in wasp venom.


In human volunteers, 5-HT was more potent (score=5000) at causing pain than DMT (less than 25), bufotenin (100), and tryptophan (0), as shown in the table below.



An animal model of pain was developed with rats. Each test chemical was injected into the paw of a rat, and the amount of swelling in the paw was measured, in terms of the thickness of the paw in millimeters. A photo of this procedure is shown below. Chemicals such as 5-HT and histamine injected subcutaneously caused local inflammation, or edema, of the paw.


Injected 5-HT to the rat paw was 200X more potent than histamine at causing edema. The graph below shows that 5-HT is more painful than histamine, causing more edema at lower doses. A mere dose of 1 ug 5-HT per paw caused a swelling reaction.


The swelling caused by 5-HT injection was prevented by pre-treatment of rats with LSD and certain phenothiazine drugs.


Reference

Lewis G. P. (Ed.) 5-Hydroxytryptamine. New York, Pergamon Press, 1958.

Doepfner W. and A. Cerletti (1958). Comparison of lysergic acid derivatives and antihistamines as inhibitors of the edema provoked in the rat's paw by serotonin. International archives of allergy and applied immunology 12, 89-97.

Sunday, April 16, 2017

LSD chromatography

The formation of a charge-transfer complex is accompanied by the appearance of a new color band. Histologists have long been interested in charge-transfer reactions for developing staining procedures based on the appearance of a visible color. For example, Romanowsky-Giemsa staining is due to azure B and eosin Y molecules, which act as electron acceptor and donor in the formation of a purple-colored charge-transfer complex.

Color tests for the detection of hallucinogenic drugs have been developed. This was shown in 1973, when twenty different hallucinogens were applied to chromatography plates and then sprayed with one of various chromogenic reagents. The formation of a color band was dependent on the electron-donating properties of the drug molecule.
“As would have been expected, the polycyclic and consequently more “electron-rich” hallucinogens, such as the harmine derivatives 6-methoxyharmalan and harmaline gave stronger colors than the simple monocyclic beta-phenylethylamines derivatives [such as mescaline, TMA, DOM, or 2,3-dimethoxy-amphetamine].” (Heacock,R.A. 1973)
The tryptamine derivatives DMT, methyltryptamine, and alpha-methyltryptamine reacted strongly with tetracyanoethylene (TCNE), an electron acceptor used as a color test reagent. Beta-carboline derivatives 6-methoxyharmalan and harmaline gave intense colors with TCNE and all electron acceptors studied. Ibogaine and LSD were easily detected with TCNE (Heacock and Forrest, 1973). The chromatographic evidence suggests that the broadly defined class of hallucinogens function as electron donors.

Erspamer was the first scientist to study serotonin in depth. His technique involved staining with the Ehrlich reaction to test for the presence of serotonin, which he called enteramine. Also referred to as Van Urk's reagent, Ehrlich's reagent is 2% dimethylaminobenzaldehyde in hydrochloric acid. It forms a purple charge-transfer complex with serotonin as well as most indoles and chlorpromazine. A purple charge-transfer complex is formed when Ehrlich's reagent is mixed with LSD. Psilocybin gives a violet color characteristic of indoles in the Van Urk reaction (A. Hofmann, 1961).


Chlorpromazine also participates in the Van Urk reaction. The Chlorpromazine-Van Urk complex has an absorption band at 520 nm, which is identical to that of the LSD-Van Urk complex. Chlorpromazine is an electron donor, so it is not surprising that chlorpromazine would form a charge-transfer reactions with the Van Urk reagent which functions as electron acceptor.
"The procedure allows for a simple, rapid, and accurate determination of small quantities of chlorpromazine." (Murty,B.S. 1970)
There are many electronic similarities between LSD and chlorpromazine. LSD and chlorpromazine both have a low transport number, and they both react with Van Urk reagent to produce a macromolecular complex with an absorption peak at 520 nm. The similarites between LSD and chlorpromazine could be related to their common anthracene-like structure, known to have exceptional electron-donating and electron-receiving properties. Though the drug effects are dissimilar, with chlorpromazine being considered to be an antipsychotic drug and LSD being considered to be one of the most powerful hallucinogen drugs known to man, they do cause a distinguishable change in awareness and may be able to provide some information about consciousness alteration by their mechanism.


Reference

Heacock R. A. and J. E. Forrest (1973). The use of electron-acceptor reagents for the detection of some hallucinogens. Journal of Chromatography 78, 240-250. 10.1016/S0021-9673(01)99063-6

HOFMANN A. (1961). Chemical pharmacological and medical aspects of psychotomimetics. Journal of experimental medical sciences 5, 31-51.Murty B. S. and R. M. Baxter (1970). Spectrophotometric determination of chlorpromazine in pharmaceutical dosage forms. Journal of pharmaceutical sciences 59, 1010-1011. 10.1002/jps.2600590721

Serotonin could have been named Enteramine



5-HT almost went by the name enteramine.

In a period between 1937 and 1940, V. Erspamer studied the enterochromaffin cells of the gut, which secrete a serum vasoconstrictor substance that he named enteramine. Erspamer detected enteramine with a color test. Its reaction with 1-nitroso-2-naphthol gave a bright violet color that he used to identify enteramine in octopod salivary glands, the thymus of some birds, and the skin of certain amphibians. Erspamer found large quantities of enteramine in the poison glands of some octopus and the stingers of wasp and bee.

Another scientist, Rapport, purified the same substance from beef blood around the same time. In 1948, Rapport published a Science paper titled "Crystalline 5-HT". In it, he wrote:
“We would like provisionally to name it serotonin, which indicates that its source is serum and its activity is one of causing constriction.” (Rapport,M.M. 1948)

Soon after, it was suggested that the names enteramine and serotonin should be dropped in favor of 5-hydroxytryptamine (5-HT). The newly purified chemical was listed as 5-HT in chemical catalogs, and soon Erspamer's enteramine became an out-dated term. Erspamer wrote:
"The name enteramine, indeed, though exact from a chemical point of view and in indicating the main source of 5-hydroxytryptamine, cannot be correctly applied to all known localizations of the substance; the name serotonin, in its turn, is inexact both from the point of view of the origin of the substance and from that of its action. In the sense, at least, intended by Rapport and his colleagues, it is by no means a “tonin”. (Erspamer,V. 1954)

Reference

Rapport M. M., A. A. Green and I. H. Page (1948). Crystalline Serotonin. Science 108, 329-330. 10.1126/science.108.2804.329

ERSPAMER V. (1954). Pharmacology of indole-alkylamines. Pharmacological Reviews 6, 425-487.

Thursday, April 13, 2017

Minimum effective brain level (MEBL) demonstrates high potency of tryptamine

Vogel and colleagues assigned a value called the minimum effective brain level (MEBL) to several hallucinogenic drugs. These researchers wanted to know the true potency of drugs, without the confounding effects of drug uptake, elimination, distribution, and biotransformation.

MEBL is defined as the brain level of a drug expressed as moles/g of brain. After receiving a drug, when a rat begins to show a significant deviation from its normal behavior, the rat is sacrificed and the drug in its brain is quantified at that point. In this case, the rat learned a conditioned avoidance response, and at a certain time after receiving LSD, it was unable to execute the learned response, e.g. to escape from a box.

The Table below lists the effective dose (left) and MEBL (right) of several different drugs. The MEBL data provides a behavioral index of drug potency, and correlates with Domelsmith's ionization potentials, thus facilitating the analysis of structure-activity relationships.


Based on MEBL criteria, diethyltryptamine, DMT, and 5-methoxy-DMT were relatively weak, and phenethanolamines were very weak. LSD and 5-methoxytryptamine were the most potent compounds tested, with MEBL 0.5 ng/g. Tryptamine plus MAO inhibition was close to 5-methoxytryptamine in potency (MEBL = 1 ng/g), thus revealing the true potency of tryptamine when its inactivating enzyme is blocked.

Vogel wrote:
"It is of interest to note that the two compounds with the highest potency, tryptamine and 5-methoxytryptamine, are naturally occurring in the mammalian brain." (Vogel,W.H. 1977)
Note that for the Table in this review paper, data was compiled across the literature, and only after many synthetic chemistry efforts and sacrificed rats later was it possible to look at the trends across different drugs. The researchers wanted to know the amount of drug in the brain and the results were very interesting in terms of what could be inferred about tryptamine and monoamine oxidase inhibitors, however as I wrote about previously, the brain is not really the target organ of LSD. Most of the LSD that enters the bloodstream ends up in the small intestine which is the place in the body with the highest amount of 5-HT receptors. Nonetheless, MEBL is an interesting way to think about dosage levels.


Reference

Vogel W. H. and B. D. Evans (1977). Structure-activity-relationships of certain hallucinogenic substances based on brain levels. Life Sciences 20, 1629-1635. doi:10.1016/0024-3205(77)90335-6

Tuesday, April 11, 2017

Sources of 5-HT in nature

5-Hydroxytryptamine (5-HT) has a widespread occurrence in nature. It occurs in plants, insect stingers, sea creatures, and mammals.
“The occurrence of 5-HT in groups so far removed from a common ancestor as vertebrates and flowering plants indicates either that the ability to produce 5-HT is primitive in evolution, or that this capacity is readily evolved as occasion demands.” (Lewis,G.P. 1958)
Table 4 (below) lists sources of 5-HT in different species. Among Vertebrates, dogs, rabbits, hens, ducks, tortoises, grass snakes, and fish have 5-HT in the gut, while in some frogs, 5-HT can be found in the skin. There is 5-HT found within the stinging fluid of some Angiosperms and Arthropoda. The 5-HT content in varies from one species to another. Remarkable also are individual variations in the same species.


Serotonin was first studied as the specific secretion product (enteramine) of the enterochromaffin cells. Located in the gastrointestinal tract, the enterochromaffin cells synthesize about 90% of the total 5-HT in the body, thus enterochromaffin cells are the primary source of 5-HT in the body. Enterochromaffin cells fluoresce after fixation with formaldehyde, showing the characteristic fluorescence reaction of 5-HT with formaldehyde. It is further indicated that enterochromaffin cells are the major source of 5-HT in the body, since some groups of fish including those from Teleostei and Cyclostomata do not contain 5-HT while other groups of fish do, and Teleostei and Cyclostomata lack enterochromaffin cells altogether (Erspamer,V. 1954).

Tunicates and echinoderms are unable to uptake radioactive 5-HT (3H-5-HT), and lack 5-HT in the gut or elsewhere. In comparison, abundant amounts of 5-HT can be found in the digestive tracts of hagfish, goldfish and bullfrog. In goldfish and bullfrog, 3H-5-HT labeling was most intense over the intestinal cells, Auerbach's plexus and the circular muscle layer.

There are high amounts of 5-HT in stomach, small intestine, and tongue. Accordingly the early 5-HT researchers believed that 5-HT was concerned with intestinal mobility. According to these researchers, enterochromaffin cells are a “diffuse endocrine organ” designed for the production and storage of 5-HT. They believed that 5-HT was released in the digestive tract and carried away by the blood stream. They also thought that high concentrations of amine oxidase in the liver were to help prevent a flooding of the general circulation with free 5-HT. Once 5-HT enters the blood stream, it is absorbed by platelets.

Another rich source of 5-HT in nature is the spleen (Table 9 below). In mammals and birds, 1 gram of spleen tissue usually contains from 2 to 7 times more than 1 mL of blood serum. The origin of 5-HT in spleen is attributed to disintegrating platelets, since the spleen is the organ that destroys platelets.


Rabbit platelets are known to contain 10X more 5-HT than human platelets. As shown in Table 9 (above), rabbit platelets have approx. 500 ug 5-HT/mL blood as compared to approx. 50 ug 5-HT/mL in human platelets. Poison salivary glands of octopus, the skin of frogs, and human carcinoid tumors are also very rich in 5-HT (Table 9 above).

Brain has relatively little 5-HT compared to other areas of the body. Brain areas richest in 5-HT are the hypothalamus, the midbrain, colliculi, grey matter of spinal cord, the medial part of thalamus and layer 4 of the cortex. It has been noted that the medial thalamus, which is connected with autonomic activity and the hypothalamus, contains a much higher concentration of 5-HT and of noradrenaline than the lateral thalamus, which relays sensory impulses to the cortex. 5-HT is also found in high quantities in area postrema, pineal organ, and cranial nerves 10 (vagus) and 12 (hypoglossal).

Finally we see in Table 9 that the highest amounts of 5-HT in nature are found in human carcinoid tumors, which are derived from enterochromaffin cells. Malignant gastrointestinal carcinoid tumors can produce excessive amounts of 5-HT in the carcinoid patient. The side effects of carcinoid tumors in humans are flushing, diarrhea, abdominal cramps, and attacks of breathing difficulties. In carcinoid patients, the 5-HT content of blood platelets and urinary excretion of 5-HIAA is consistently elevated, leading to flushed skin. Episodes of flushing are thought to be accompanied by an increased release of 5-HT from the tumor, as explained below.
"Intravenous injections of serotonin in both control and carcinoid subjects were followed by flushes of the skin similar to spontaneous attacks occurring in the carcinoid patient and by pressor responses of 29 to 58 mm Hg systolic and 9 to 57 mm Hg diastolic. The flush, involving the face, neck, and extremities, was intense in 4 patients and mild in 1. Subjective discomfort was profound in all subjects and characterized by nausea, paresthesias, breathlessness, and an urge to empty the bowel and bladder. These effects were transient and lasted for about the same length of time, 2 to 3 minutes, as the rise in arterial pressure." (Schneckloth,R. 1957)
In patients with carcinoid tumors in whom the peripheral production of 5-HT is excessive, no particular mental effects can be described. It is interesting to consider their symptoms, since there is some question about the significance of high 5-HT levels in organisms. As described above in the quote by Schneckloth, delivery of intravenous 5-HT to the already hyperserotonemic patients caused a flushing reaction. This fits with what is known about serotonin as a vasoconstrictor.

The sources of serotonin in nature indicate that it has an important role in the digestive and circulation system.


Reference

ERSPAMER V. (1954). Pharmacology of indole-alkylamines. Pharmacological Reviews 6, 425-487.

SCHNECKLOTH R., I. H. PAGE, F. DEL GRECO and A. C. CORCORAN (1957). Effects of serotonin antagonists in normal subjects and patients with carcinoid tumors. Circulation 16, 523-532. 

SJOERDSMA A., H. WEISSBACH, L. L. TERRY and S. UDENFRIEND (1957). Further observations on patients with malignant carcinoid. The American Journal of Medicine 23, 5-15.10.1016/0002-9343(57)90353-4

Lewis G. P. (Ed.) Symposium on 5-hydroxytryptamine (1957: London). New York: Pergamon Press, 1958.

Collier H. O. J. 1958. The occurrence of 5-hydroxytryptamine (HT) in nature; In 5-Hydroxytryptamine, Lewis G. P. (Ed.), New York: Pergamon Press, pp. 5-19.

Domelsmith 7, relationship of hallucinogenic activity to ionization potential

Predictions of drug hallucinogenicity have been made based on two parameters: the ionization potential energy and lipophilicity. The lipophilicity parameter is critical because if a drug molecule cannot be absorbed by the membranes of the body, it is not expected to reach the target receptor. The ionization potential energy has an empirical relationship on its own with effective drug dose. Despite huge simplifications, those two parameters can predict drug effects.
“The model here arises from a reduction of variables until the molecule in the isolated state remains as the governing structure dictating the magnitude of observable phenomena. The extraction of structure-activity relationships from this model leads to information which is necessarily limited by certain exclusions of reality, but which is frequently the most attainable kind of relationship.” (Kier,L.B. 1978)
Domelsmith studied the ionization potentials of LSD, several psychoactive tryptamines, and amphetamines including DOM. The ionization potential was significantly correlated with the quantities of drug needed to displace LSD binding from rat brain membranes (-log ED50). Out of 5 drugs plotted here, LSD is the most potent binder to rat brain membranes, and the best electron donor with average ionization potential energy=7.65 eV. This plot includes mescaline (5), DMT (4), and LSD (1), regarded as structurally different types of hallucinogens.




There are many dissimilarities in chemical structure between LSD (1), chlorpromazine (2), promethazine (3), DMT (4), and mescaline (5), yet there is a trend toward better electron-donating ability with the more planar and rigid drugs.



In another series of correlations, the average of the first and second ionization potential energies was plotted versus Vogel's minimum effective brain level (MEBL), a measure of hallucinogen activity in rats. Out of 10 drugs, LSD (1) had the lowest ionization potential and the highest biological potency (MEBL).



The next figure shows the same plot, with labels beside each data point. The unsubstituted compounds phenethylamine (PA) and amphetamine (A) are the least potent psychotomimetics and have the largest ionization potential energies (~9 eV), while LSD and 5-methoxy-tryptamine (5MT) are the most potent in terms of MEBL and have the smallest ionization potential energies (~7.5 eV). Note that plain tryptamine plus MAO inhibition (T) is plotted and represents one of the most potent drugs in terms of IP and MEBL.



The electron-donating ability of the LSD molecule itself deserves special attention. It is thought that the productive binding of a drug to its receptor is responsible for the primary biological response, but embodied within this index of receptor binding are other relationships more directly related, as Domelsmith, Houk, and Kier have shown. A correlation between drug potency in humans and 5-HT2 receptor affinity reflects in part the drug's HOMO energy.


Reference

Kier L. B. Molecular orbital theory in drug research, Vol. 10 of Medicinal chemistry series, de Stevens G. (Ed.), New York: Academic Press, 1971.

Domelsmith L. N., L. L. Munchausen and K. N. Houk (1977). Lysergic acid diethylamide. Photoelectron ionization potentials as indices of behavioral activity. Journal of Medicinal Chemistry 20, 1346-1348.

Domelsmith 8, harmaline ionization potentials

LN Domelsmith investigated the ionization potential energies of LSD and harmala alkaloids. Table II summarizes the first four pi ionization potential energies, ranging from 7.38-10.5 electron volts (eV), for norharmane, harmane, harmol, harmine, and harmaline. Harmaline was the best electron donor in this series, with a first ionization potential energy of 7.38 eV.


Dihydro-harmine (harmaline) and harmine differ by 2 electrons, the saturation of one bond, which in this case changed the energy of the ionization potential by 0.5 eV, a very large quantity.


The trend continues that harmine and harmaline are the most psychoactive in this series of harmala alkaloids, and have the lowest energy ionization potential.


Reference

Domelsmith L. N. and K. N. Houk (1978). Photoelectron spectroscopic studies of hallucinogens: the use of ionization potentials in QSAR. NIDA Research Monograph 22, 423-440.

Saturday, April 08, 2017

HOMO calculations of phenothiazines

Molecular orbital calculations of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies reflect the electron-donating and electron-accepting properties of a molecule.

In a seminal paper in 1959, Karreman et al. suggest that the neuroleptic properties of chlorpromazine are related to the unique negative K value (K=-0.217) obtained for its HOMO. Their work extended that of the Pullmans, who had found a negative K value for FMNH2, the reduced form of flavin monocleotide (FMN).  Karreman also found a negative K value for phenothiazine (K=-0.210), indicating the the strong donor properties of chlorpromazine would be linked to its phenothiazine rings. There is a lot of structural similarity between phenothiazine, chlorpromazine, and FMNH2. 

Methods for calculating HOMO and LUMO energies of a molecule have become more advanced over the years.  There do not seem to be many researchers who focus on the so-called ``negative K values'' that were discussed with some excitement in 1959.  It is accepted however that phenothiazine is a good electron donor.

In more recent work by Cogordan et al., the HOMO energies of several tricyclic antidepressants and neuroleptics were calculated with 3 different methods, referred to as the RHF, LSD, and SE-AM1 methods. The drugs studied were promazine, chlorprothixene, chlorpromazine, dibenzepine, amitriptyline, imipramine, clomipramine and opipramol. These eight drugs have a phenothiazine-like structure in common.


When the HOMO energies of these drugs were calculated using the RHF method, all values were between 7.4-8.87 electron volts (eV). HOMO values for these drugs ranged from 7.36-8.34 eV using the SE-AM1 method. These HOMO energies, obtained theoretically, are similar to the ionization energies of phenothiazine drugs obtained experimentally with photoelectron spectroscopy.



Most of the drugs studied have Nitrogen or Sulfur on the main ring. Out of this series of eight, promazine consistently had the smallest absolute value for HOMO energy.
“The contribution to the HOMO and LUMO from the atomic orbitals of the Nitrogen in the central ring is remarkable.” (Cogordan,J.A. 1999)


Reference

KARREMAN G., I. ISENBERG and A. SZENT-GYORGYI (1959). On the mechanism of action of chlorpromazine. Science 130, 1191-1192. doi:10.1126/science.130.3383.1191

Cogordan J. A., M. Mayoral, E. Angeles, R. A. Toscano and R. Martinez (1999). Neuroleptic and antidepressant tricyclic compounds: Theoretical study for predicting their biological activity by semiempirical, density functional, and hartree-fock methods. International journal of quantum chemistry 71, 415-432.

Friday, April 07, 2017

Domelsmith 6, photoelectron spectra of 4,5-methylenedioxy-DMT

In 1982, Domelsmith and colleagues studied 5 dimethyl-tryptamine (DMT) analogs with photoelectron spectroscopy. The compounds studied were 4,5-methylenedioxy-DMT (first ionization potential, 7.25 eV), 5,6-methylenedioxy-DMT (7.46 eV), 4-methylthio-DMT (7.43 eV), 5-methylthio-DMT (7.68 eV), and 6-methylthio-DMT (7.52 eV). Figure 1 shows the photoelectron spectra of methylenedioxy- and methylthio-substituted DMT.


Methylthio substitution of DMT at the 4- or 6-position enhanced the electron donating properties of the drug. These experiments with photoelectron spectroscopy confirm the importance of attachment at the 4-position, for example psilocin is 4-hydroxy DMT. Compared to 5- or 6-methylthio-DMT, the drug 4-methylthio-DMT had the most favorable configuration, with a first ionization potential energy of 7.43 eV, compared with the parent molecule DMT (first ionization potential energy, 7.57 eV).

The readers of this blog may know that 5-methoxy-DMT is a very powerful hallucinogen. Methoxy groups often have the effect of lowering the ionization potential energy, but in these studies the first ionization potential energies of 5-methoxy-DMT (7.61 eV) and 5-methylthio-DMT (7.68 eV) were slightly higher in energy than the parent molecule DMT (first ionization potential energy=7.57 eV), suggesting that the 5-methoxy groups on DMT may confer bioavailability rather than electron-donating ability.

Methylenedioxy-substituted DMT analogs were even better electron donors than methylthio-substituted DMT molecules. The electronic configuration of 4,5-methylenedioxy-DMT is very interesting because it is the only tryptamine studied by Domelsmith with an ionization potential energy equal to 7.25 eV, which is equivalent to the first ionization potential energy of LSD. These two drugs are different structurally, see below, but they have the same electron-donating ability.


It is noteworthy that 4,5-methylenedioxy-DMT had the lowest ionization potential of the 5 DMT analogs, and it was the most rigid tryptamine studied. This is a clue to the potential importance of a rigid planar structure for electron donation. Another way to see the effects of planarity on the ionization potential is to compare between 4,5-dimethoxy-amphetamine and 4,5-methythlenedioxy-amphetamine.


4,5-dimethoxy-amphetamine (above left) has one planar and one perpendicular methoxy group, whereas oxygens from the methylenedioxy group (above right) are both in the plane of the ring. Conformational constraint in 4,5-methylenedioxy-amphetamine would force the p orbitals of oxygen into more overlap with the planar pi system; this configuration has a pi system that will eject a single electron or pair of electrons with slightly less external perturbation than the pi system of 4,5-dimethoxy-amphetamine. The first ionization potentials energies of 4,5-dimethoxy-amphetamine and 4,5-methylenedioxy-amphetamine are close, but the methylenedioxy compound is a slightly better electron donor by 0.02 eV.

Reference

Kline T. B., F. Benington, R. D. Morin, J. M. Beaton, R. A. Glennon, L. N. Domelsmith, K. N. Houk and M. D. Rozeboom (1982). Structure-activity relationships for hallucinogenic N,N-dialkyltryptamines: photoelectron spectra and serotonin receptor affinities of methylthio and methylenedioxy derivatives. Journal of Medicinal Chemistry 25, 1381-1383. 10.1021/jm00353a021

Domelsmith 4, photoelectron spectra of phenothiazines

Many antipsychotic drugs have a phenothiazine group, which is an excellent electron donor. In 1977, Domelsmith studied phenothiazine, N-methyl-phenothiazine, promazine, chlorpromazine, thioridazine, and trifluoperazine with photoelectron spectroscopy.  There was some question about whether neuroleptic properties are related to low ionization potentials and good electron donating ability, but the first ionization potential was insufficient to predict antipsychotic activity in this series, so the hypothesis was not validated.

Phenothiazine, N-methyl-phenothiazine and promazine have 4-5 ionization bands from pi orbitals, which come from pi orbitals and correspond to 4 very clear peaks in the photoelectron spectra (Figure 3), and range in energy from 7.26-10.43 eV. The first two ionization potentials at 7.26 eV and 8.35 eV were assigned to central Nitrogen and Sulfur pi orbitals, which are significantly delocalized over the whole ring.



The photoelectron spectra of chlorpromazine, thioridazine, and trifluoperazine are shown below. Thioridazine, with 2-position methylthio, has the lowest ionization energy (7.00 eV) studied in Domelsmith's research, meaning that its electrons are very much on the fringe. Like promazine, the first and second ionization potential bands are assigned to the ring Sulfur and Nitrogen. In chlorpromazine, the 2-position Chlorine atom gives rise to a band at 11.24 eV. The trifluoromethyl groups in position-2 of trifluoperazine were not as electron withdrawing as predited by calculations. Trifluoperazine's first ionization potential energy of 7.31 eV was slightly higher than that of phenothiazine, 7.26 eV.



Nitrogen methylation tended to enhance the overall electron-donating ability of the molecule, as revealed by comparison between phenothiazine (first ionization potential energy, 7.26 eV) and N-methyl-phenothiazine (7.15 eV). A similar trend was observed in the tryptamine series; a Nitrogen side chain ionization potential was lowered from 9.25 eV in tryptamine, to 8.9 eV in N-methyl-tryptamine, to 8 eV in N,N-dimethyl-tryptamine.



Thioridazine (first ionization potential, 7.00 eV) surpassed chlorpromazine (7.16 eV), and LSD (7.25 eV) as an electron donating molecule. The results for the phenothiazine series are summarized in Table I (above).


Reference

Domelsmith L. N., L. L. Munchausen and K. N. Houk (1977). Photoelectron spectra of psychotropic drugs. 2. Phenothiazine and related tranquilizers. Journal of the American Chemical Society 99, 6506-6514. doi:10.1021/ja00462a007

Domelsmith 2, photoelectron spectra of LSD, DMT, indole, and several tryptamines

The photoelectron spectra of DMT and LSD is pictured below. The lowest pi ionization potential of LSD (7.25 eV) is slightly lower than that of N,N-DMT (7.57 eV).


The photoelectron spectrum of LSD revealed 7 ionization potentials between 7.25 and 9.75 eV. Four ionization potentials are assigned to the pi ring system; they are 7.25, 8.05, 8.5, and 9.75 eV. The other 3 ionization potentials of LSD are assigned to the diethylamide group. The amine lone pair ionization energy is 8.4 eV. The carbonyl-nitrogen gives rise to the peak in the 8.8 eV region of the spectra, while the carbonyl pi orbital gives rise to an ionization potential at 9.08 eV.

In the photoelectron spectrum of DMT, 3 ionization potentials are assigned to the pi ring system, and 1 ionization potential energy to the nitrogen lone pair on the side-chain. The pi ionization potentials of DMT occur at 7.6, 8.2, and 9.5 eV, and the tertiary amine lone pair gives rise to an an ionization near 8 eV.

Figure 7 below shows the photoelectron spectra of indole, tryptamine, N-methyl-tryptamine, N,N-dimethyl-tryptamine, 5-methyl-tryptamine, and 5-methoxy-tryptamine.



Tryptamines have a side chain bearing a nitrogen with lone pair orbitals. The ionization potential energy of the nitrogen lone pair falls consistently near 9.0 eV. In the tryptamine spectra, the broad band centered at 9.25 eV is attributed to ionization from the nitrogen lone pair. This ionization potential is lowered from 9.25 eV in tryptamine, to 8.9 eV in N-methyl-tryptamine, and finally to around 8 eV in N,N-dimethyl-tryptamine. Thus we see that the degree of carbon bulk on the side-chain nitrogen, not just the aromatic moiety, can significantly affect the electron-donating ability of the nitrogen lone pair.

In Table I, the first (IP1) and second (IP2) ionization potential energies of several tryptamines are summarized. LSD is the best electron donor in this series, followed by DMT.



Reference

Domelsmith L. N., L. L. Munchausen and K. N. Houk (1977). Photoelectron spectra of psychotropic drugs. 1. Phenethylamines, tryptamines, and LSD. Journal of the American Chemical Society 99, 4311-4321. doi:10.1021/ja00455a018

Tuesday, April 04, 2017

Charge-transfer mechanism of drugs 2.

The electron-donating tendency of a molecule can be expressed in terms of the energy of its outermost HOMO electron, which is determined theoretically, or its ionization potential energy, which can be measured with a piece of lab equipment called a photoelectron spectrometer. There is good agreement between HOMO values and the ionization potential energy, adding to the predictive value of molecular orbital theory. From Kier, the figure below shows that Ehomo is related to ionization potential energy in electron volts.



The next figure shows a similar linear relationship, except that ionization potential energy is now plotted on the x-axis with Ehomo energies on the y-axis. The chemicals studied were phenethylamines and tryptamines.



The kHOMO and ionization potential energy have been studied with interest because the values can be used to predict whether a certain reagent is likely to participate in a chemical reaction, or form a charge-transfer complex. For example, in the next figure, the energy of formation of a donor-acceptor complex is linearly related to the HOMO energy of the electron donor molecule. An experiment was performed where the electron donors naphthalene (1), phenanthrene (2), pyrene (3), anthracene (4), and naphthacene (5), were mixed with electron acceptors trinitrobenzene (TNB), trinitrofluorenone (THF), and tetracyanoquinodimethane (TCNQ). Each electron donor molecule was mixed with an electron acceptor molecule, and the energy of formation was measured. The plot shows that the kHOMO of the electron donor is correlated to the energy of formation of different charge-transfer complexes.



These results show that a charge-transfer reaction relies, to a great extent, on the tendency of the electron donor molecule to part with one of its electrons.


Reference

Kier L. B. Molecular orbital theory in drug research. Academic Press, New York, 1971.

Ariens E. J. Drug design. Medicinal chemistry series, de Stevens G. (Ed.), Academic Press, New York, 1971.

Domelsmith L. N., L. L. Munchausen and K. N. Houk (1977). Photoelectron spectra of psychotropic drugs. 1. Phenethylamines, tryptamines, and LSD. Journal of the American Chemical Society 99, 4311-4321.

Sunday, December 06, 2015

LSD charge-transfer complexes 3. LSD-riboflavin

Hallucinogenic agents are probably electron donors in some key step involving a charge-transfer complex with a biological acceptor molecule entity. Previously I covered the topic of electrostatic and charge-transfer forces in LSD-TCNE and LSD-NAD+ small molecule complexes. This article will present studies on a LSD-riboflavin complex.

In 1958, Isenberg and Szent-Gyorgyi mixed LSD-25 with riboflavin-5'-phosphate and observed a red color at –78 C. They discovered that the riboflavin molecule had taken up one electron from LSD. LSD was functioning as an electron donor in the formation of riboflavin charge-transfer complexes; the transferred electron to reduce riboflavin comes from the pi-electron pool of the LSD indole system. In the same publication, the authors discuss tryptopan-riboflavin, 5-HT-riboflavin, and 1-methyl-medmain-riboflavin complexes, all of which led to the appearance of a red color at -78 C. The results are shown in Table 1 below.



Histidine-riboflavin or tyrosine-riboflavin did not give a red color, indicating that no charge-transfer complex had been formed, and that histidine and tyrosine are inferior in electron-donating ability compared to drugs such as tryptophan and LSD. There were variations among the drugs which formed a charge-transfer complex with riboflavin. For example, the 5-HT-riboflavin complex was 7X stronger than the tryptophan-riboflavin complex indicating that serotonin was a better electron donor than tryptophan.

Some tissues such as liver have a great quantity of strongly bound riboflavin. The brown color of the liver can be attributed to the flavin radical formed in a charge-transfer interaction with liver protein. If liver tissue becomes cancerous, it takes on a different balance of reductive and oxidative processes and changes color.


Reference

Isenberg I. and A. Szent-Gyorgyi (1958). FREE RADICAL FORMATION IN RIBOFLAVIN COMPLEXES. Proceedings of the National Academy of Sciences U. S. A. 44, 857-862. doi:10.1073/pnas.44.9.857

LSD charge-transfer complexes 2. LSD-NAD+

The electron acceptor NAD+ forms a charge-transfer complex with LSD, in which an electron is transferred from the highest occupied molecular orbital (HOMO) of the LSD pi system to the lowest empty molecular orbital of NAD+.

The charge-transfer process is accompanied by the appearance of a new absorption band. In 1967, Fulton and colleagues studied the wavelength of the absorption maximum of NAD+ charge-transfer complexes.

“We have shown that NAD+ of concentration 1.03E-2M, when mixed with fairly strong electron donors, such as substituted pteridines, uric acid, serotonin creatine sulphate, lysergic acid, and phenothiazines, gave solutions which were coloured yellow to orange because of the formation of charge-transfer complexes." (Fulton,A. 1967)

Some of the electron donor molecules studied were LSD, indole, uric acid, promazine, and promethazine, and different absorption maximums were obtained for each donor-NAD+ complex as shown in Table 1 below. Also the researchers measured the ionization potential energies of the electron donors, and found that LSD had an ionization potential of 7.8 electron Volts, indole (7.9 eV), uric acid (7.5 eV), promazine (7.2 eV), promethazine (7.2 eV), and chlorpromazine (7.3 eV).



The authors found that the absorption maximum of the charge-transfer complex correlated reasonably with the ionization potential of the electron donor drug, but not so well with the energies of the HOMO, perhaps because there are many approximations involved in the theoretical studies of the HOMO energy. However other groups have found a correlation between the absorption maximum and kHOMO energies.

As listed in Table 1 above, the LSD-NAD+ charge-transfer complex had an absorption maximum at 340 nm, which is the absorption maximum of the native LSD molecule. This compares to the 520 nm absorption maximum that is characteristic of LSD-TCNE or LSD-Ehrlich complexes.


Reference

Fulton A. and L. E. Lyons (1967). Electron-accepting strength of NAD+. Australian Journal of chemistry 20, 2267-2268.

LSD charge-transfer complexes 1. LSD-tetracyanoethylene

The electron donor molecule LSD forms a charge-transfer complex with the electron acceptor tetracyanoethylene (TCNE). The charge-transfer complex has a characteristic absorption band, allowing the detection of the presence of LSD. When LSD or other hallucinogen drugs are applied to a silica gel plate and then sprayed with either TCNE or other electron acceptor drugs, a color band is detected.

In 1968, Millie and colleagues studied the electronic properties of methoxylated indoles and tryptamines by their ability to form charge-transfer complexes with TCNE or 1,3,5-trinitrobenzene (TNB), another electron acceptor. Many indoles and phenothiazines form a charge-transfer complex with TCNE or TNB; the wavelength of the absorption maximum of the complex is often between 300-720 nm. As shown in the figure below, the authors found a correlation between the absorption maximum of the acceptor-TCNE or acceptor-TNB complexes and kHOMO values of the donator indoles and tryptamines. The x-axis is the kHOMO while the y-axis is 1000/lambda, where lambda is the maximum absorption wavelength of the charge-transfer reaction product.


1-methyl-LSD was among the indoles and phenothiazines that were tested. The charge-transfer complex of TCNE and 1-methyl-LSD (letter p, Figure 1 above) had an absorption maximum at 520 nm. As determined by Huckel calculations, 1-methyl-LSD had kHOMO=0.487. This kHOMO value is larger than Ehomo=0.218 obtained for LSD by Karreman in 1959, though on the whole these values suggest good electron donating ability. According to the figure above, the electron-donating ability of 1-methyl-LSD (p) lies between 4-methoxy-indole (i) and 6-methoxy-indole (k).

TCNE-bezene complexes are used to study the electron-donating properties of different benzene derivatives

There is no mystery about the physical and chemical forces that bind a hallucinogen drug to biological receptors. The forces may be compared with the physical and chemical forces that bind TCNE to benzene or indoles. For example, the ionization potential of an electron donor molecule can predict the rate of formation of its drug-TCNE complex, as shown by Domelsmith et al. in 1977. Several different benzene derivatives were mixed with the electron acceptor TCNE, and the rate of formation of benzene-TCNE complexes was measured. When the apparent enthalpy of formation of the benzene-TCNE complexes was plotted versus the average of the first and second ionization potential energies of the benzene molecules, an excellent linear correlation was obtained (Figure 12 below).


Quantum mechanics is the method used to calculate the kHOMO energy. The dose of structurally diverse hallucinogens to produce consciousness alteration is correlated with the drug's kHOMO value, so it is very likely that quantum electronic properties of matter play a role in the mechanism of consciousness alteration.


Reference

Fulton A. and L. E. Lyons (1967). Electron-accepting strength of NAD+. Australian Journal of Chemistry 20, 2267-2268.

Millie P., J. P. Malrieu, J. Benaim, J. Y. Lallemand and M. Julia (1968). Researches in the indole series. XX. Quantum mechanical calculations and charge-transfer complexes of substituted indoles. Journal of Medicinal Chemistry 11, 207-211. 10.1021/jm00308a003

Domelsmith L. N., L. L. Munchausen and K. N. Houk (1977). Photoelectron spectra of psychotropic drugs. 1. phenethylamines, tryptamines, and LSD. Journal of the American Chemical Society 99, 4311-4321.