Synthesis of N,N1-disubstitutedbisbenzimidazolesulphides of Potential Pharmacological Interest

S. Srinivas Rao, Ch. Venkata R

Abstract

2-(1-chloroethyl)-1H-benzimidazole (1a, i.e. 1, R=H) on condensation with (1H-benzimidazol-2-yl)methanethiol (2a, i.e. 2, R1=H) in methanol using triethylamine as a base under reflux for 3 hrs yielded bis((1H-benzimidazol-2- yl)methyl)sulfane (3a, i.e. 3, R=R1=H) which on alkylation using two equivalents of alkylating agent in dimethylformamide (DMF) as solvent and K2CO3 as a base using tetra-n-butylammonium bromide (TBAB) as phase transfer catalyst (PTC) gave N,N1-dialkylbisbenzimidazolesulphides 3b-e. Alternatively, 3b-e could also be prepared by condensing 2-(1-chloroethyl)-1-alkyl-1H-benzimidazole (1b-e, i.e. 1, R=methyl, ethyl, benzyl and n-butyl) and (1- alkylbenzimidazol-2-yl)methanethiol (2b-e, R1= methyl, ethyl, benzyl and n-butyl) in a single step. Using this synthetic strategy, N,N1- unsymmetricallydialkylbisbenzimidazolesulphides 3f-q were prepared either by condensing 2-(1-chloroethyl)-1H-benzimidazole (1a, i.e. 1, R=H) with (1-alkylbenzimidazol-2-yl)methanethiol 2b-e, i.e. R1=alkyl1 to obtain 3 (R=H, R1=alkyl1) followed by alkylation under PTC conditions or by condensing 1a (i.e. 1, R=alkyl) with N-unsubstituted-2-mercaptobenzimidazole (2a, i.e. 2 , R1=H) to yield 3 (R= alkyl1, R1=H) followed by alkylation under PTC conditions. Direct condensation of N-substituted-2-(1-chloroethyl)-1H-benzimidazole (1be, i.e. 1, R=alkyl) with (1-alkylbenzimidazol-2-yl)methanethiol 2b-e, i.e. 2, R1=alkyl1) also gave the respective 3f-q.