Conformations and lipophilicity profiles of some cyclic beta-(1 -> 3)- andbeta-(1 -> 6)-linked oligogalactofuranosides

The conformational features of cyclooligosaccharides composed of beta-(1 -- > 3)- and beta-(1 --> 6)-linked galactofuranose units, i.e., cyclo[D-Galf b eta-(1 --> 3)](n) with n = 4 (1) and 5 (2), and cyclo[D-Galf beta-(1 --> 6) ](n) with n = 3 (3) and 4 (4), were investigated by means of Monte Carlo si mulations. The flexibility of the macrocyclic backbone strongly favors bent and asymmetrical conformations over round geometries. Generation of the mo lecular surfaces of the global minimum-energy structures reveals disk-type shapes for 1-4 without through-going central cavities, yet distinct indenta tions close to the O-2/O-3 groups, respectively. The molecular lipophilicit y patterns prove these surface dents to be hydrophobic for the beta-(1 --> 6)-linked cyclogalactans 3 and 4, whereas their beta-(1 --> 3)-linked count erparts display an inverse situation with a hydrophobic outer core structur e. (C) 1999 Elsevier Science Ltd. All rights reserved.