Novel [(diazomethyl)carbonyl]-1,2,3,4-tetrahydronaphthalene derivatives as potential photoaffinity ligands for the 5-HT1A receptor.

The photolabile (diazomethyl)carbonyl function was introduced into the 8-position of 2-(N,N-di-n-propyl-amino)-1,2,3,4-tetrahydronaphthalene in three ways, resulting in the ether 8-[[(diazomethyl)carbonyl]methoxy]-2-(N,N-di-n-propylamino)-1,2,3,4- tetrahydronaphthalene (2), the ester 8-(diazoacetoxy)-2-(N,N-di-n-propyl-amino)-1,2,3,4- tetrahydronaphthalene (3), and the ketone 8-[(diazomethyl)carbonyl]-2-(N,N-di-n-propylamino)- 1,2,3,4-tetrahydronaphthalene (4). Specific binding of these compounds at the 5-hydroxytryptamine1A sites in rat brain membranes labeled with 1 nM [3H]-8-hydroxy-2-(N,N-di-n-propylamino)- 1,2,3,4-tetrahydronaphthalene (8-OH-DPAT) showed IC50 values of ca. 75, 125, and 25 nM, respectively, for the three compounds. Photolysis of methanolic solutions of 2-4 in the absence of receptor proteins lead in each case to an abundance of Wolff-rearranged products. In the case of ether 2, subsequent beta-elimination to 8-OH-DPAT removed this compound from serious consideration as a photoaffinity ligand. Ester 3 and ketone 4 were photolysed in vitro. Whereas ester 3 was ineffective in decreasing the specific binding of [3H]-8-OH-DPAT, ketone 4 decreased 40% of the specific binding of [3H]-8-OH-DPAT in the presence (but not the absence) of ultraviolet light. Thus this ketone emerges from these studies as a good candidate for a photoaffinity label for the 5-hydroxytrypatamine1A receptor.

Structure-activity relationships in potentially hallucinogenic N,N-dialkyltryptamines substituted in the benzene moiety.

A series of N,N-dialkyltryptamines with methylthio or methylenedioxy substituents in the 4, 5, and 6 positions and methyl or isopropyl on the side-chain nitrogen has been synthesized. The behavioral pharmacology of these compounds showed them to possess Bovet-Gatti profiles characteristic of hallucinogens, and the 5-methylthio congener was the most potent. Binding studies at [3H]LSD and [3H]5-HT sites demonstrated that no single structural feature correlated with binding or behavioral changes and suggest a complex mode of action for these potential hallucinogenic agents.

Structure-activity relationships for hallucinogenic N,N-dialkyltryptamines: photoelectron spectra and serotonin receptor affinities of methylthio and methylenedioxy derivatives.

Serotonin receptor affinity and photelectron spectral data were obtained on a number of substituted N,N-dimethyltryptamines. Evidence is presented that electron-donating substituents in the 5-position lead to enhanced behavioral disruption activity and serotonin receptor affinity as compared to unsubstituted N,N-dimethyltryptamine and analogues substituted in the 4- or 6-position. Some correlation was found between ionization potentials and behavioral activity, which may have implications concerning the mechanism of receptor binding.

Pyroglutamyl diazomethyl ketone: potent inhibitor of mammalian pyroglutamyl peptide hydrolase.

Pyroglutamyl peptide hydrolase (EC 3.4.11.8), a cysteine protease, cleaves the N-terminal pyroglutamyl residue from pyroglutamyl peptides such as thyrotropin releasing hormone. Pyroglutamyl diazomethyl ketone was synthesized as an active site directed inhibitor. Preincubation of the partially purified bovine brain enzyme with nanomolar concentrations of inhibitor produced rapid inactivation. Inhibitor concentrations five orders of magnitude higher did not inactivate other exo- and endopeptidases. A dose of 0.1 mg/kg administered intraperitoneally to mice totally inactivated the enzyme in all tissues studied including brain. Pyroglutamyl diazomethyl ketone should be of value in studies on the physiological role of this enzyme in the metabolism of pyroglutamyl-containing peptides.

5-Oxoprolinal: transition-state aldehyde inhibitor of pyroglutamyl-peptide hydrolase.

Pyroglutamyl-peptide hydrolase (EC 3.4.11.8) removes the N-terminal pyroglutamyl residue from pyroglutamyl-containing peptides such as thyrotropin-releasing hormone (TRH), luteinizing hormone-releasing hormone (LH-RH), neurotensin, and bombesin. The aldehyde analogue of pyroglutamate, 5-oxoprolinal, was synthesized as an active site directed transition-state inhibitor of the enzyme. 5-Oxoprolinal was found to be a potent (Ki = 26 nM) and specific competitive inhibitor of pyroglutamyl-peptide hydrolase. Other aldehydes tested inhibited the enzyme only weakly or not at all. 5-Oxoprolinal blocked the degradation of LH-RH by purified pyroglutamyl-peptide hydrolase. The inhibitor, when injected into mice, inhibited the enzyme after 10 and 30 min. 5-Oxoprolinal should be of value in studies probing the biological significance of pyroglutamyl-peptide hydrolase.