Simple and Efficient Synthesis of Novel 3-Substituted 2-Thioxo-2,3-dihydro-1H-benzo[g]quinazolin-4-ones and Their Reactions with Alkyl Halides and α-Glycopyranosyl Bromides

A series of 3-substituted 2-thioxo-2,3-dihydro-1H-benzo[g]quinazolin-4-ones 4a-e were synthesized from the reaction of 3-aminonaphthalene-2-carboxylic acid 1 with isothiocyanate derivatives 2a-e. The alkylation of 4a-e with alkyl halides gave 3-substituted 2-alkylsulfanyl-2,3-dihydro-1H-benzo[g]quinazolin-4-ones 5a-o. S-Glycosylation was carried out via the reaction of 4a-e with glycopyranosyl bromides 7a and 7b under anhydrous alkaline conditions. The structure of the compounds was established as S-nucleoside and not N-nucleoside. Conformational analysis has been studied by homonuclear and heteronuclear two-dimensional NMR methods (2D DFQ-COSY, heteronuclear multiple quantum coherence, and heteronuclear multiple bond correlation). The S site of alkylation and glycosylation was determined from the H-1 and C-13 heteronuclear multiple quantum coherence experiments.