Chiral recognition by sulfoxides. Induced circular dichroism from symmetric mesobilirubin analogs

Abstract

Symmetric analogs of mesobilirubin-XIIIα, with propionic acid groups shortened and lengthened, exhibit induced circular dichroism (ICD) in CH 2Cl 2 solvent with excess S-(−)-methyl- p-tolylsulfoxide. The dimethyl esters of mesobilirubins with acetic, propionic, butyric, valeric and caproic acid chains at C-8 and C-12 all give essentially the same bisignate ICD, with Δϵ max 420 ⋍ +13, Δϵ max 376 ⋍ −10. However, the bisignate ICD of the free acids varies from Δϵ max 436 = −11, Δϵ max 393 = +6 to Δϵ max 425 = +14, Δϵ max 379 = −11 according to the length of the alkanoic acid chains.