Title
Chiral Recognition by CD-Sensitive Dimeric Zinc Porphyrin Host. 1. Chiroptical Protocol for Absolute Configurational Assignments of Monoalcohols and Primary Monoamines
Author
Tibor Kurtán, Nasri Nesnas, Yuan-Qiang Li, Xuefei Huang, Koji Nakanishi, Nina Berova
Year
2001
Journal
JACS
Abstract
A general microscale protocol for the determination of absolute configurations of primary amino groups or secondary hydroxyl groups linked to a single stereogenic center is described. The chiral substrates are linked to the achiral trifunctional bidentate carrier molecule (3-aminopropylamino)acetic acid (1, H2NCH2CH2CH2NHCH2COOH) and the resultant conjugates are then complexed with dimeric zinc porphyrin host 2 giving rise to 1:1 host/guest sandwiched complexes. These complexes exhibit exciton-coupled bisignate CD spectra due to stereodifferentiation leading to preferred porphyrin helicity. Since the chiral sense of twist between the two porphyrins in the complex is dictated by the stereogenic center of the substrate, the sign of the couplet determines the absolute configuration at this center. The twist of the porphyrin tweezer in the complex can be predicted from the relative steric sizes of the groups flanking the stereogenic center, such that the bulkier group protrudes from the complex sandwich. In certain α-hydroxy esters and α-amino esters, electronic factors and hydrogen bonding govern the preferred conformation of the complex, and hence the CD spectra.
Full Article
Instrument
J-720, 810
Keywords
Circular dichroism, Absolute configuration