Synthesis and 13C NMR chemical shift assignments of 2,2'-bipyridine-4,4'-dicarboxylates of bile acid methyl esters

Abstract

Novel 2,2'-bipyridine-4,4'-dicarboxylates 3a-3d of four bile acid methyl esters have been synthesized from 2,2'-bipyridine-4,4'-dicarboxylic acid 1 and the corresponding bile acid methyl esters (methyl lithocholate 2a, methyl chenodeoxycholate 2b, methyl deoxycholate 2c, and methyl cholate 2d). In addition to the desired products, 3α -(2,6-dichlorophenylcarboxy) bile acid methyl esters 4a-4d were obtained. The structures of 3a-4d have been ascertained by 1 D 1 H and 13 C NMR, 2 D PFG 1 H, 13 C HMQC, and MALDI TOF MS. Molecular weights and 13 C NMR chemical shifts of 3a-4d have been presented. The geometry of 3a has been optimized semi- empirically at the PM3 level and it has been observed that the minimum energy structure of 3a is a open type conformation due to lack of attractive intramolecular electrostatic interactions between the heads of the molecule which would have favoured the formation of cleft type structure. The synthesized bipyridine-bile acid conjugates are interesting structures from the molecular recognition point of view because they could have potential to form complexes with some transition metal ions, for example with silver, cadmium, and ruthenium.