Absolute stereochemical determination of chiral carboxylates using an achiral molecular tweezer.

A new type of molecular tweezer (1) has been synthesized for the direct determination of the absolute configuration of chiral carboxylates without analyte derivatization. Upon the addition of diamine and anionic guests, 1 exhibited shifts in its absorption spectrum with clear isosbestic points. The continuous variation method indicated that both the diamine and anionic guests form 1:1 host-guest complexes with 1 with very high binding affinity. When Boc-L-Ala (BLA) as a form of tetrabutylammonium salt was added to 1, a weak negative CD signal was observed. This weak CD signal was dramatically changed to a strong positive CD couplet upon addition of achiral 1,12-diaminododecane. Such a positive CD couplet was observed for all of the tested L-amino acid derivatives, while the D-amino acid derivatives gave the opposite signals. As a result of these unique characteristics of 1, it can be utilized as a highly sensitive probe for the absolute stereochemical determination of chiral carboxylates.