Hemicarbasucrose: turning off the exoanomeric effect induces less flexibility.

Hemicarbasucrose, a close congener of sucrose in which the endocyclic oxygen atom of the glucose moiety is replaced by a methylene group was synthesized for the first time. The conformational behaviour of hemicarbasucrose was studied by a combination of molecular mechanics and NMR spectroscopy (J and NOE data). It was shown that the carbadisaccharide populates two distinct conformational families in solution, the normal syn-psi conformation, which is the predominating conformation of the parent natural O-glycoside, and the anti-psi conformation, which has not been detected for the O-disaccharide. Interestingly, the hemicarbasucrose is less flexible than its natural congener.