Henry Rapoport

The reaction of the psoralens with deoxyribonucleic acid

Psoralen photochemistry is specific for nucleic acids and is better understood at the molecular level than are all other methods of chemical modification of nucleic acids. These compounds are used both for in vivo structure analysis and for photochemotherapy since they easily penetrate both cells and virus particles. Apparently, natural selection has selected for membrane and virus penetrability during the evolution of these natural products. Most cells are unaffected by relatively high concentrations of psoralens in the absence of ultraviolet light, and the metabolites of the psoralens have thus far not created a problem. Finally, psoralens form both monoadduct and cross-links in nucleic acid helices, the yield of each being easily controlled by the conditions used during the photochemistry.

Methyllycaconitine and (+)-anatoxin-a differentiate between nicotinic receptors in vertebrate and invertebrate nervous systems

Specific high‐affinity binding sites for 125I‐α‐bungarotoxin and (−)‐[3H]nicotine have been measured in rat brain and locust (Schistocerca gregaria) ganglia. The binding sites for 125I‐α‐bungarotoxin had similar K d values of 1.5 × 10−9 and 0.8 × 10−9 M for rat and locust preparations, respectively; the corresponding values for the (−)‐[3H]nicotine‐binding site were 9.3 × 10−9 and 1.7 × 10−7 M. Methyllycaconitine (MLA) potently inhibited 125I‐α‐bungarotoxin binding in both rat and locust. MLA was a less effective inhibitor of (−)‐[3H]nicotine binding whereas (+)‐anatoxin‐a was a very potent inhibitor at this site in the rat but not in the locust. These data suggest that (+)‐anatoxin‐a is a useful probe for the high‐affinity nicotine‐binding receptor in vertebrate brain, whereas MLA is a preferential probe for the subclass of receptor that binds α‐bungarotoxin.

Structure of a psoralen-thymine monoadduct formed in photoreaction with DNA☆

Abstract A photoreaction product between calf thymus DNA and 8-methoxypsoralen, a naturally occurring psoralen, was hydrolyzed with acid to isolate a major species of the reaction, 8-methoxypsoralen-thymine monoadduct. The crystal structure of the monoadduct has been determined. The structure confirms the results of other spectroscopic studies and allows one to conclude or suggest that: (1) the photoreaction occurs preferentially at both T-A and A-T sequences in natural DNA; (2) the photocrosslink introduces a substantial kink in the DNA structure; (3) the configuration of the photoproduct is “cis-syn” at both ends of the psoralen; (4) the thymine and psoralen moieties remain planar even after the photoreaction; and (5) the angle between psoralen and thymine in the photoproducts is not fixed but has a limited range of flexibility.

Effect of deuteration of N--CH3 group on potency and enzymatic N-demethylation of morphine.

Substitution of deuterium for the N-methyl hydrogens of morphine produced a significant reduction in the potency and lethality of morphine in mice regardless of the route of administration. There was no effect on the time of onset, maximal effect, or duration of action. N-demethylation by rat liver microsomal enzymes was characterized by a smaller reaction rate constant, a higher energy of activation, and a larger Michaelis constant with respect to the deuterated morphine. These findings indicated that deuteration of the N-methyl group of morphine not only caused reduction in potency, but also a reduction in the rate of oxidative N-demethylation, and a distinct weakening of the binding to the enzyme active centers.

A photochemical characterisation of reactions of psoralen derivatives with DNA.

Psoralens are nucleic acid photoreagents which form mono-and diadducts to pyrimidine bases upon irradiation with long wavelength ultraviolet light (Musajo et al., 1967). Diaddition results in the formation of interstrand bridges or crosslinks in nucleic acid dou ble helices (Cole, 1970, 1971). Crosslink formation is a multistep process involving initial dark binding or intercalation of the psoralen, photoaddition of the psoralen to a pyrimidine base forming a monoadduct followed by conversion of the monoadduct to crosslink by a second photoaddition to a second pyrimidine base. Each of these steps may be investigated as a function of the type and position of the substituents of a given psoralen compound.

The occurrence of saxitoxin and other toxins in various dinoflagellates

A number of dinoflagellate species, previously reported to be toxic, were cultured and collected from natural blooms. Saxitoxin, detected by chemical assay and mouse bioassay, was absent in all dinoflagellates except Gonyaulax catenella and Gonyaulax excavata. Toxins other than saxitoxin were observed in Gymnodinium breve, Amphidinium carteri, Gonyaulax excavata and Gonyaulax catenella by means of fish and mouse bioassays. Most dinoflagellates tested were non-toxic. A sample of Mytilus edulis (blue mussels) collected during a red tide in Spain was found to contain an appreciable amount of a toxin which appears to be saxitoxin.

Biosynthesis of the nicotine alkaloids in Nicotiana glutinosa. Interrelationships among nicotine, nornicotine, anabasine, and anatabine.

Abstract Biosyntheses from 14 CO 2 carried out with both intact Nicotiana glutinosa plants and seedlings have demonstrated that nornicotine is not the precursor of nicotine in either the root or the aerial portions of the plant. This conclusion contrasts with that reached on the basis of 3 H incorporations into the alkaloids of Nicotiana rustica . The most probable relationship, based on 14 CO 2 biosyntheses and supporting some previous conclusions, is that nornicotine arises by demethylation of nicotine in both the root and aerial portions. The relative specific activities of anabasine and anatabine after the 14 CO 2 biosyntheses indicated that anabasine is not the precursor of anatabine. In the case of nicotine, nornicotine, anatabine, and anabasine, higher specific activities were noted in the samples isolated from the root than in those isolated from the aerial portions. This shows that these four alkaloids all can be formed in the Nicotiana root, and furthermore, since the 14 C in these experiments first enters into the metabolism of the aerial portion of the plants, these results indicate that the N. glutinosa root is the most active site of formation of each of these alkaloids. Finally, a comparison of the specific activities of anabasine, anatabine, and nicotine suggests that if a precursor-product relationship exists among these alkaloids it must be nicotine → anatabine or anabasine, or both.

The vinylketene acetal route to aklavinone and 11-deoxydaunomycinone

Abstract 11-Deoxyanthracyclinone precursors 6a and 6b have been prepared regiospecifically by the reaction of bromojuglone methyl ethers 4a and 4b with vinylketene acetal 5 , prepared from the Hagemanns ester ketal 7a .

Biosynthesis of Camptotheca acuminata alkaloids

Abstract Tracer feeding experiments with Camptotheca acuminata plants show that [1′- 14 C] L -tryptophan, [Ar- 3 H 4 ] L -tryptophan, [Ar- 3 H 4 ,1′- 14 C]tryptophan, [1′- 14 C]-tryptamine, [2- 14 C] DL -mevalonate, and [2- 14 C]geraniol-[2- 14 C]nerol are incorporated into camptothecin. Direct stem injection of the labeled precursors into C. acuminata plants resulted in a substantial increase in the activity of isolated Camptotheca alkaloids as compared to root feeding of the same tracer.

MORPHINAN ALKALOIDS IN PAPAVER BRACTEATUM. BIOSYNTHESIS AND FATE

The known metabolic pathway for hydrophenanthrene alkaloids in Papaver somniferum has been examined for occurrence in P. bracteatum, a species reported to contain thebaine but no codeine or morphine. 1,2-Dehydro-reticulinium-[3-14C] chloride and (±)-reticuline-[3-14C] were fed to P. bracteatum plants and both were incorporated, the former into reticuline and thebaine and the latter into thebaine, suggesting that thebaine biosynthesis is the same in the two species. Studies of the natural abundance of morphinan alkaloids in P. bracteatum and the results from feeding codeinone-[16-3H] and codeine-[16-3H] indicate that this species can reduce codeinone to codeine but can not perform either of the demethylations to produce codeinone or morphine. Fed thebaine-[16-3H] was substantially metabolized but not by pathways that involved demethylations to either oripavine or northebaine.