01931nas a2200193   4500008004100000022001400041245012800055210006900183260010600252300001600358490000700374520110400381100002201485700002401507700002401531700003001555700002001585856013201605       2008                        eng d  a0040-402000aDiastereoselective addition of planar N-heterocycles to vinyl sulfone-modified carbohydrates: a new route to isonucleosides0 aDiastereoselective addition of planar Nheterocycles to vinyl sul  aTHE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLANDbPERGAMON-ELSEVIER SCIENCE LTDcNOV  a10406-104160 v643 a<p>Michael-type addition reactions of planar N-heterocycles at the C-2 positions of vinyl sulfone-modified carbohydrates provide an efficient and general route for the carbon-N-heterocycle bond formation. Therefore, the addition pattern of planar heterocycles, such as imidazole, triazole, thymine, and adenine to 3-C-phenyisulfonyl-hex-2-enopyranosides (1 alpha/1 beta) and 3-C-p-toluenesulfonyl-pent-2-enofuranosides (2 alpha/2 beta) was studied for developing a general methodology for the synthesis of new classes of isonucleosides possessing a carbon-N-heterocycle linkage at C-2 positions of furanosyl and pyranosyl sugars. To a great extent, the anomeric configurations of the starting vinyl sulfones play crucial roles in deciding the diastereoselectivity of addition of heterocycles. However, the trityl protected 3-C-p-toluenesulfonyl-hex-2-enopyranosides (33 alpha/33 beta) were judged to be More practical starting materials for desulfortylation and deprotection for the synthesis of a new class of thymine and adenine deoxyisonucleosides. (C) 2008 Elsevier Ltd. All rights reserved.</p>1 aSanki, Aditya, K.1 aBhattacharya, Rahul1 aAtta, Ananta, Kumar1 aSuresh, Cheravakkattu, G.1 aPathak, Tanmaya  uhttps://library.ncl.res.in/content/diastereoselective-addition-planar-n-heterocycles-vinyl-sulfone-modified-carbohydrates-new-001853nas a2200205   4500008004100000022001400041245017600055210006900231260007100300300001200371490000700383520098900390100002401379700002601403700001901429700002301448700002901471700002001500856012701520       2010                        eng d  a0022-326300aExperimental and theoretical study on the remarkable influence of protecting groups on the selectivity of addition of amines to vinyl sulfone-modified hex-2-enopyranosides0 aExperimental and theoretical study on the remarkable influence o  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJAN  a303-3140 v753 a<p>Although phenylmethylene-protected vinyl sulfone-modified carbohydrate 2 alpha reacts with both primary and secondary amines in Michael fashion to afford aminated products, only primary amines react with the dibenzyl-protected 3 alpha, 6-O-trityl-protected 4 alpha, and unprotected 5 alpha, highlighting for the first time the remarkable influence of protecting, groups on the reaction patterns of vinyl sulfone-modified carbohydrates. The quantum chemical calculations suggest that the Michael addition of amines and proton transfer to vinyl sulfone-modified carbohydrates 2 alpha and 5 alpha are possible via relay process in a concerted mechanism. These calculations reveal that the addition of primary amines to vinyl sulfone-modified carbohydrate is preferential due to the low activation energy barriers, whereas the addition of secondary amines has relatively higher activation energy barriers. The theoretical conclusions are in line with the experimental observations.</p>1 aBhattacharya, Rahul1 aKesharwani, Manoj, K.1 aManna, Chinmoy1 aGanguly, Bishwajit1 aSuresh, Cheravakattu, G.1 aPathak, Tanmaya  uhttps://library.ncl.res.in/content/experimental-and-theoretical-study-remarkable-influence-protecting-groups-selectivity-0