Chiral recognition of cyclic α-hydroxyketones by CD-sensitive zinc tetraphenylporphyrin tweezer



A combined chemical/chiroptical microscale protocol for the determination of absolute configurations of cyclic α-hydroxyketones is described. The hydroxyl group in cyclic α-hydroxyketones is converted into (3-aminopropylamino)acetate (NH2CH2CH2CH2NHCH2COOR), or more generally, according to a newly developed protocol, into (3-hydroxypropylamino)acetate group (HOCH2CH2CH2NHCH2COOR). The resultant conjugated compound forms a 1:1 host–guest complex with a dimeric zinc porphyrin tweezer, which exhibits exciton-coupled bisignate CD spectrum centered around the 420-nm porphyrin Soret band due to induced helicity between the two porphyrins in the complex. The absolute configurations of the α-stereogenic center is then determined by comparison of the sign of the observed CD exciton couplet of the complex with that of the preferred porphyrin twist predicted by the Merck Molecular Force Field (MMFFs) method. Chirality 17:305–315, 2005. © 2005 Wiley-Liss, Inc.