Metal-Free Heterogeneous Photocatalysis for Carbocarboxylation of Alkenes: Efficient Synthesis of γ-Amino Carboxylic Derivatives.

A metal-free heterogeneous protocol is established herein for the synthesis of value-added γ-amino acid scaffolds via carbocarboxylation of alkenes with CO2 and alkylamines under visible light irradiation. The protocol shows broad substrate scope under mild reaction conditions and good stability of the catalyst for recycle tests. Moreover, the methodology could be feasible to the late-stage derivatization of several natural products, enriching the chemical arsenal for practical application.

Synthesis and biological evaluation of 2- and 7-substituted 9-deazaadenosine analogues.

A series of 2-halogen and 7-alkyl substituted analogues of 9-deazaadenosine and 2'-deoxy-9-deazaadenosine was synthesized by new efficient methodology involving transformation of corresponding 9-deazaguanosine and 2'-deoxyguanosine, which in turn were synthesized by direct C-glycosylation of 1-benzyl-9-deazaguanine with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose and methyl 2-deoxy-3,5-di-O-(p-toluoyl)-D-ribofuranoside, respectively. Deoxychlorination of C6 and diazotization/chloroor fluoro-dediazoniation of the sugar-protected 9-deazaguanosine, followed by selective ammonolysis at C6 and deprotection of the sugar moiety, gave 2-chloro- and 2-fluoro-9-deazaadenosine (6 and 9). Substitution of the 7-position of the dihalogen-intermediate with alkyl groups, followed by ammonolysis and deprotection, provided 2-chloro-7-alkyl-9-deazaadenosines (13a-e) and 2-fluoro-7-benzyl-9-deazaadenosine (13f). Catalytic hydrogenation of 13a-e gave 7-alkyl-9-deazaadenosines 14a-e. Similarly, 2-chloro-2'-deoxy-9-deazaadenosine (21), 2-chloro-2'-deoxy-7-methyl-9-deazaadenosine (25), 2'-deoxy-9-deazaadenosine (22), and 2'-deoxy-7-methyl-9-deazaadenosine (26) were prepared from sugar-protected 2'-deoxy-9-deazaguanosine. Among these compounds, 7-benzyl-9-deazaadenosine (14b) showed the most potent cytotoxic activity, with IC50 values of 0.07, 0.1, 0.2 and 1.5 microM, while both 7-methyl-9-deazaadenosine (14a) and 2-fluoro-9-deazaadenosine (9) also demonstrated significant cytotoxic activity with IC50 values of 0.4, 0.7, 0.3, and 1.5 microM, and 1.5, 0.9, 0.3, and 5 microM against L 1210 leukemia, P388 leukemia, CCRF-CEM lymphoblastic leukemia, and B16F10 melanoma cells, respectively.

Synthesis and biological evaluation of 2',3'-didehydro-2',3'-dideoxy-9-deazaguanosine, a monophosphate prodrug and two analogues, 2',3'-dideoxy-9-deazaguanosine and 2',3'-didehydro-2',3'-dideoxy-9-deazainosine.

2',3'-Didehydro-2',3'-dideoxy-9-deazaguanosine (1), its monophosphate prodrug (2), and two analogues, 2',3'-dideoxy-9-deazaguanosine (3) and 2',3'-didehydro-2',3'-dideoxy-9-deazainosine (4), have been synthesized from benzoylated 9-deazaguanosine (5). Basic hydrolysis of 5, selective protection of the 2-amino and 5'-hydroxy functions with isobutyryl and silyl groups, respectively, followed by reaction with thiocarbonyldiimidazole gave the cyclic thiocarbonate, which, upon reaction with triethyl phosphite, followed by deprotection, afforded 1. Treatment of 1 with phenyl methoxyalaninylphosphochloridate and N-methylimidazole gave 2. Catalytic hydrogenation of 1 gave 3. Hydrodediazoniation of 1 with tert-butyl nitrite and tris(trimethylsilyl)silane gave 4. Compounds 1-4 were found to be inactive against the human immunodeficiency virus and exhibited minimal to no cytotoxic activity against the L1210 leukemia, CCRF-CEM lymphoblastic leukemia, and B16F10 melanoma in vitro.

4-nitrobenzyloxycarbonyl derivatives of O(6)-benzylguanine as hypoxia-activated prodrug inhibitors of O(6)-alkylguanine-DNA alkyltransferase (AGT), which produces resistance to agents targeting the O-6 position of DNA guanine.

A series of 4-nitrobenzyloxycarbonyl prodrug derivatives of O(6)-benzylguanine (O(6)-BG), conceived as prodrugs of O(6)-BG, an inhibitor of the resistance protein O(6)-alkylguanine-DNA alkyltransferase (AGT), were synthesized and evaluated for their ability to undergo bioreductive activation by reductase enzymes under oxygen deficiency. Three agents of this class, 4-nitrobenzyl (6-(benzyloxy)-9H-purin-2-yl)carbamate (1) and its monomethyl (2) and gem-dimethyl analogues (3), were tested for activation by reductase enzyme systems under oxygen deficient conditions. Compound 3, the most water-soluble of these agents, gave the highest yield of O(6)-BG following reduction of the nitro group trigger. Compound 3 was also evaluated for its ability to sensitize 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine (laromustine)-resistant DU145 human prostate carcinoma cells, which express high levels of AGT, to the cytotoxic effects of this agent under normoxic and oxygen deficient conditions. While 3 had little or no effect on laromustine cytotoxicity under aerobic conditions, significant enhancement occurred under oxygen deficiency, providing evidence for the preferential release of the AGT inhibitor O(6)-BG under hypoxia.

Evaluation of 3-deaza-adenosine analogues as ligands for adenosine kinase and inhibitors of Mycobacterium tuberculosis growth.

OBJECTIVES: Analyse a series of halogenated 3-deaza-adenosine analogues for efficacy against Mycobacterium tuberculosis H37Ra and determine if adenosine (Ado) kinase plays a role in the mechanism of action of these compounds. METHODS: The MIC as determined by microdilution broth assay provided a measure of antitubercular efficacy. MIC values were measured in M. tuberculosis strains H37Ra, SRICK1 (an Ado kinase-deficient strain of M. tuberculosis derived from H37Ra) and SRICK1 complemented with adoK, the gene which codes for Ado kinase in M. tuberculosis, in order to determine if Ado kinase played a role in the mechanism of action of these compounds. Furthermore, each compound was analysed as both a substrate and inhibitor for purified Ado kinases from M. tuberculosis and human sources. RESULTS: 2-Fluoro-3-deaza-adenosine, 3-fluoro-3-deaza-adenosine and 2,3-difluoro-3-deaza-adenosine exhibited antitubercular activity that was Ado kinase-dependent. Furthermore, these compounds were at least 10-fold better substrates for M. tuberculosis Ado kinase than the human homologue. CONCLUSIONS: The Ado kinase-dependent antitubercular activity exhibited by several of the halogenated 3-deaza-adenosine analogues investigated in this study warrants further investigation of these compounds as antitubercular agents. Furthermore, substrate and inhibition studies provided insight into the Ado-binding domain of Ado kinase, indicating that steric hindrance may limit the size of exocyclic modifications at the 3-position of Ado.