MOLECULAR RECOGNITION .18. COMPLEXATION OF CHIRAL GLYCOLS, STEROIDAL POLYOLS, AND SUGARS WITH A MULTIBENZENOID, ACHIRAL HOST AS STUDIED BY INDUCED CIRCULAR-DICHROISM SPECTROSCOPY - EXCITON CHIRALITY INDUCTION IN RESORCINOL ALDEHYDE CYCLOTETRAMER AND ITS USE AS A SUPRAMOLECULAR PROBE FOR THE ASSIGNMENTS OF STEREOCHEMISTRY OF CHIRAL GUESTS

Resorcinol-dodecanal cyclotetramer 1 as an achiral host in chloroform forms hydrogen-bonded complexes with a variety of chiral di(poly)ols (2-24) including steroids and sugars. The complexation processes can be followed very conveniently by the induced circular dichroism (CD) spectroscopy. The binding constants as determined by CD titration increase in the order 15 (steroidal monool, K = 8.7 M-1) < 3, 6, and 8 (acyclic glycols, (4.9-7.1 x 10) < 9-alpha, 10-alpha, 12, and 13 (cyclic glycols and steroidal diols, (0.94-2.7) x 10(2)) < 11 (steroidal triol, 6.9 x 10(2)). This order reflects the extents of multiple host-guest hydrogen-bonding interactions. All of the resulting complexes exhibit CD with split Cotton effects as a result of exciton chirality induction in otherwise symmetric 1 upon binding of a chiral guest. The signs of split Cotton effects for complexes derived from glycols are correlated with the chiralities or absolute configurations of the guests, while those for sugar complexes are governed by the ring conformations (C1 or 1C) of sugar pyranoses. These results suggest that host 1 can be used as a novel, supramolecular probe for the assignments of stereochemistry of chiral guests.