Evidences of Strong C−H····O Bond in a ortho-Carboranyl β-Lactoside in Solution

The existence of short intermolecular C-HââââO interactions has been established since the early 1960s for several molecules though IR1 and X-ray crystallography.2,3 Following these observations a variety of theoretical studies, based on semiempirical and ab initio molecular orbital approaches, have been reported for a series of C-HââââX (X ) O, N, Cl, F, P, S) hydrogen bonds.4,5 Recently, a role for C-HââââO bonds in stabilizing cohesive forces within biological macromolecules has been proposed.6-8 This unusual interaction has therefore a great interest. However, very few experimental evidences have been found for the presence of C-HââââO bonds in solution.9,10 In this study we found a strong intramolecular C-HââââO bond in lactosyoxymethyl-o-carborane (LCOB, Chart 1),11,12 a potential agent for boron neutron capture therapy (BNCT),13 by using NMR spectroscopy. In particular, results showed that the interaction took place between the activated C2-H of the carboranyl cage14 and the anomeric oxygen of the glucose ring of lactose (O1¢). This hypothesis was confirmed by ab intio quantum mechanical calculations.