Novel unsymmetrical leuco-TAM, (2E, 2 ' E)-2,2 '-{(E)-4-phenylpent-2-ene-1,5-diylidene}bis(1,3,3-trimethylindoline) derivatives: Synthesis and structure elucidation

Abstract

Novel unsymmetrical leuco-TAM, (2E, 2'E)-2,2'-{(E)-4-phenylpent-2-ene-1,5-diylidene}bis(1,3,3-trimethylindoline) derivatives were synthesized from a reaction of commercially available 2-methylene-1,3,3-trimethylindoline (FB) and substituted cinnamaldehyde derivatives. The chemical structures of the resulting molecules were determined using 1D and 2D NMR spectroscopy experiments, including COSY, HMBC and NOESY. The compounds had the EEE configuration and were potent precursors for Cy5 TAM(+) dyes. This is different from the Malachite green FB-analogs, which generally have a ZE configuration and are precursors to Cy3 TAM(+) dyes. The formation of unsymmetrical LTAM molecules as the sole product suggests that the Michael-type addition of a FB molecule occurs on the delta-carbon of the alpha, beta, gamma, delta-unsaturated imminium salts, which were formed as an intermediate at the first step. (C) 2011 Elsevier Ltd. All rights reserved.