Resonance assignments of diastereotopic CH 2 protons in the anomeric side chain of selenoglycosides by means of 2 J(Se,H) spin-spin coupling constants Yury Yu. Rusakov, a Leonid B. Krivdin, a * Ambati Ashok Kumar, b László Szilágyi b and Katalin E. Kövér b Unambiguous resonance assignments of diastereotopic CH 2 protons in the anomeric side chain of nine alkyl- and aralkylselenoglycosides have been carried out on the basis of experimental CPMG-HSQMBC measurements and theoret- ical second order polarization propagator approach (SOPPA) calculations of geminal 77 Se- 1 H spin-spin coupling constants involving diastereotopic pro-R and pro-S protons. Theoretical conformational analyses have been performed at the MP2/6-311G** level. The conformational space of each of the selenoglycosides under study could be adequately described as a mixture of six interconverting conformers with the molar fractions depending on the nature of the side chain substituent at the selenium atom. The good agreement observed between measured and the weighted conformational averaged values of the calculated coupling constants provides a basis for reliable diastereotopic assignments in this type of carbohydrate structures. Copyright © 2012 John Wiley & Sons, Ltd. Keywords: NMR; selenoglycosides; diastereotopic assignment; 77 Se- 1 H spin-spin coupling constants; SOPPA; CPMG-HSQMBC; carbohydrate; selenium Introduction Selenosugars deserve attention in various aspects. Methyl Se-hexosaminides have been identified in 2002 as the first Se-containing sugar metabolites in rat urine and liver [1] and subsequently reported in human urine as well. [2] Also, carbohydrate ligands containing a heavy Se atom were found to be useful in solving the phase problem in X-ray crystallography of carbohydrate-binding proteins [3] or in biochemical investigations of glycosidase enzymes as hydro- lytically stable glycoside mimics. [4] In carbohydrate chemistry selenoglycosides [5] are extensively utilized as stable glycosyl donors for oligosaccharide syntheses. [6] Detailed structural characterization of selenosugars, their glycosidic conforma- tions in particular, is therefore of high interest and practical value. In our previous publication [7a] we have carried out a combined experimental and theoretical study of 2 J(Se,H) spin-spin coupling constants involving the anomeric proton in the pyranose ring of three representative selenoglycosides to perform conformational analysis in respect to the internal rotation around the anomeric C 1 -Se bond. In the present study, we use 2 J(Se,H) couplings involving the side chain methylene protons, measured experimentally and calculated theoretically, for the unambiguous diastereotopic assignment in the anomeric side chain of nine selenoglyco- sides 1–9. Experimental measurements of 2 J(Se,H) are performed using the low-power CPMG-HSQMBC technique, as described in our previous publications [7] , whereas all calculations of 77 Se- 1 H couplings are carried out within a general second order polariza- tion propagator approach (SOPPA), [8] which recently has been extensively used for the high-level calculations of different types of spin-spin coupling constants – in a large number of saturated * Correspondence to: Leonid Krivdin, A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1 Favorsky St., 664033 Irkutsk, Russia. E-mail: krivdin_office@irioch.irk.ru a A.E. Favorsky Irkutsk Institute of Chemistry, Russian Academy of Sciences, Irkutsk, Russia b Department of Chemistry, University of Debrecen, Debrecen, Hungary Magn. Reson. Chem. 2012, 50, 488–495 Copyright © 2012 John Wiley & Sons, Ltd. Research Article Received: 21 January 2012 Revised: 26 March 2012 Accepted: 13 April 2012 Published online in Wiley Online Library: 16 May 2012 (wileyonlinelibrary.com) DOI 10.1002/mrc.3824 488