The C-H center dot center dot center dot O(sp3) hydrogen bond in trisialic acid lactones has been examined by using long-range COSY (LRCOSY) and ab initio calculations. From an analysis of the LRCOSY spectra, (3)J correlations of (B)H(ax)(9)/(A)H(8) and (C)H(ax)(9)/(B)H(8) confirmed the existence of hydrogen-bond connections of (x+1)C(9)-(x+1)H(ax)(9)center dot center dot center dot(x)O(8). The theoretical bond energy of the hydrogen bond was estimated to be 1.0 or 1.6 kcal/mol by using two models. The acid-catalyzed cooperative lactonization of oligosialic acids can be understood in terms of the additional C-H center dot center dot center dot O(sp3) stabilization in the lactone product. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
