Tmc,hd,on: Asymf?y Vol. 5, No. 12 PP. 2325-2334. 1994 Ekevier scimee La F’rinted in Gnat Britain 0957-4166!94 $7.aJto.00 0957-4166(94)00313-O zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO Influence of Intramolecular Hydrogen-Bonding on the Conformational Properties of Sugar Thioureas Carmen Ortiz Mellet, Albert0 Moreno Marfn, Jo& L. Jim6nez Bhutco, Jo& M. Garefa FemBndez*, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP and Joa6 Foe&es* Dqmiamentc de Qafmica Organica, Facultsd de Qufmica, Universid& de &villa, Apartadu 553, R-41071 Sevilla,Spain. Absmt: Reaction of deoxyisothiccyaaato derivatives of 1,2:3,4-G-0-isoprupylidenea-D-galactopyranose.. lf:3j~-O-isopropyla-~~~ , aad 23:4JdiX%qxopylidareg-D-fructepyrauose with ammonia affordedthe cenespcudiag sugarUricureas. Roth zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ the 2 and zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP E stereoisomers around the NH-C(=S) bond were observed in the lH aad 13C NMRspectra of the later ia thelow temperature range, their relative proportions beinga function of the sugar configuration. Experhnental evidence for the existence of seven-membered NW-0 in@an~okcular hydrogen bonds in theE isomers of thioureas hasbeenobtained from DNMR experiments, rotatieasl barrier heightcalculations, measmements of tempemhue coefficients for the lH chemical shiftsof the NH si@s. audstudy of theinfluence of the solvent puliuity iu themtamedc ratio. Thioureido sugars are important intermediates in synthetic approaches to nucleoside analogues. In addition, the structural analogy of the thiourea group with other functional groups commonly found in naturally occurring carbohydrate derivatives, such as amide, urea, or phosphate, make sugar thioureas interesting from a biological point of view. For this reason, much effort has been directed to the synthesis of such compounds.1 However, works dealing with the configuration and conformation of sugar thioureas are scarce,tu~e in spite of the infhtence that these structural aspects may have on both the chemical and biological properties. Previous studies concerned exclusively the particular case of a thioureido group linked to a secondary carbon atom of an acylated aldopyranose. The conformational rigidity of the sugar ring simplifies the structural analysis of these molecules. We now report the synthesis and conformational properties of some thioureido sugars in which the functional group is linked to a primary carbon atom. The existence of two slow-rotating pseudo amide bonds in these compounds makes the structural analysis more complex as compared to the homologous thioamides2. On the other hand, the sharing of delocalized 1~ electrons leads tc much lower energy barriers suitable to study by using dynamic NMR techniques.3 The possibility of hydrogen bonding as a consequence of the relative flexibility of the tbiotneidomethyl group and its role in the stabilization of certain conformers as a function of the sugar conQuration have been studied. 2325