Paper Citing NAMD - Abstract
Kahle, C.; Deubner, R.; Schollmayer, C.; Scheiber, J.; Baumann, K.; Holzgrabe, U.
NMR spectroscopic and molecular modelling studies on cyclodextrin-dipeptide inclusion complexes
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8, 1578-1589, APR 15 2005
Cyclodextrins (CDs) are often used to separate the enantiomers of chiral drugs by HPLC, GC, and capillary electrophoresis (CE). For dipeptides containing one aromatic amino acid, a reversal of the migration order is observed in CE upon increasing the pH value of the background electrolyte from 2.5 to 3.5. In order to understand the mechanism of chiral recognition of this phenomenon, NMR experiments, namely complexation-induced chemical shifts (CICS) and ROESY, were performed. Comparing the CICSs obtained for the pairs Diac-beta-CD/Ala-Phe and HDAS-beta-CD/Ala-Phe and Diac-beta-CD/Ala-Tyr and HDAS-beta-CD/Ala-Tyr revealed very small changes, thereby indicating a rather weak interaction of the respective guest molecules with their host. The CICS for beta-CD and HS-beta-CD confirmed an inclusion of the aromatic moiety into the CD cavity. It is shown that, at pH 2.5, the D,Denantiomer of Ala-Tyr immerses deeper into the cavity of beta-cyclodextrin than the L,L-enantiomer, and this was subsequently confirmed by molecular dynamics simulations. Furthermore, at pH 3.5 the immersion is shallower, as shown by the H-1 and ROESY NMR findings and confirmed by the molecular dynamics simulations. The immersion depths of the dipeptides were calculated by defining a plane in the cavity to gain information about the different behaviour of the studied chemical species. The employed procedure is easily generalised to other host-guest complexes and is expected to improve data evaluation in other cases, too. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).
