ONE POT SYNTHESIS OF ARSONOLIPIDS<i>VIA</i>THIOARSENITE PRECURSORS

Abstract

Abstract Reduction of the racemic and optically active 1,2-dihydroxypropyl-3-arsonic acids by thiophenol gives the chloroform soluble phenyl esters of rac-, (R-, and (S)-1,2-dihydroxypropyl thioarsonous acids which are acylated by fatty acid chlorides/pyridine to give the racemic and optically active arsonolipids (1,2-diacyloxypropyl-3-arsonic acids). The yields of long chain arsonolipids are significantly higher than those reported from the acylation of salts of 1,2-dihydroxypropyl-3-arsonic acid. The yield of short chain arsonolipids are lower, partly because of difficulties in removing traces of coprecipitated fatty acids. The esters of alkylthioarsonous acids are decomposed by carboxylic acids and on silica gel and a mechanism for their acylation is proposed. The melting points of arsonolipids [(R) = (S) > rac] increase smoothly with the fatty chain length while the enthalpies of fussion [(R) > (S) > rac] show a maximum at 1,2-dimyristoyloxypropyl-3-arsonic acid. The thermal behaviour of the aqueous dispersions of short chain arsonolipids, suggests that their head groups are not easily hydrated because of strong intermolecular hydrogen bonding of the head groups.