No abstract

Four β‐cyclodextrins (CDs) were prepared bearing either an (N,N‐dimethylamino)propylamino group (1), an (N‐methyl)‐piperazino group (2) or a benzylamino group (3), or seven methylamino susbtituents (4). Association constants K in water with di‐ and tripeptides reach up to 200 M −1, and after protection at the N‐terminus up to 680 M −1. Appreciable binding occurs only in the presence of lipophilic amino acid side‐chains, with preference for this at the C‐terminus. A moderate sequence and side‐chain selectivity is observed with 1, 2 and 3, but less so with the highly charged 4 where ion pairing dominates. Detailed NMR analyses with advanced techniques including T‐ROESY and GHSQC allow full assigment of most 1H and 13C signals, with extraction of many substituent and complexation induced shifts changes (SIS and CIS values, respectively). The CIS values and NOE cross peaks from ROESY experiments provide for insight into the binding modes of selected complexes, indicating, e.g., the simultaneous presence of complexes with a peptide phenyl unit approaching from both the narrow and the wide side of the CD cavity. With 3 one observes self‐inclusion of the pendant phenyl ring within the cavity, and its replacement by analytes such as peptides, or by adamantanecarboxylic acid. The inclusion modes are illustrated with force field simulated structures and many NMR spectra, which are made available in electronic supplements. Copyright © 2001 John Wiley & Sons, Ltd. Additional material for this paper is available from the epoc website at http://www.wiley.com/epoc: (NMR shift tables; 3D coordinates for molecular structures; 1D‐ and 2D‐NMR spectra)

Equilibrium constants of complexes between β-cyclodextrin and glucose, galactose, or mannose have been determined by fluorometric competition titrations in water to be as low as K = 1 – 0.5 M−1, in sharp contrast to recently published values for glucose around K = 400 M–1. The pentoses ribose, xylose, and arabinose show association constants between 6.3 and 1.5 M−1, in agreement with published values. Preliminary computer-aided molecular modelling studies suggest that the small values observed for the hexoses are not due to steric hindrance of an intracavity inclusion but to a smaller number of intermolecular hydrogen bonds and to some strain as a result of cyclodextrin deformation. Calorimetric measurements of the glucose–β-cyclodextrin complex show, again in contradiction with the literature, an endothermic reaction, or a free enthalpy value close to zero. Key words: cyclodextrin complexes, sugar complexation, glucose complexation, calorimetry, computer-aided molecular modelling.

organic chemistry, review organic chemistry, review Z 0200 39 -313 NMR Studies of Cyclodextrins and Cyclodextrin Complexes -[323 refs.]. -(SCHNEIDER, H.-J.; HACKET, F.; RUEDIGER, V.; IKEDA, H.; Chem. Rev. (Washington, D. C.) 98 (1998) 5, 1755-1785; Fachrichtung Org.