1 H NMR Conformational Study of a Variety of -Anomers of C5-Substituted 2'-Deoxyuridines: Comparison to Their Antiherpetic  Counterparts Jaroslaw Poznan ´ ski,* , † Krzysztof Felczak,* Maria Bretner,* Tadeusz Kulikowski,* and Mieczyslaw Remin‡ ,1 *Institute of Biochemistry and Biophysics, Polish Academy of Sciences, ul. Pawinskiego 5a, 02-106 Warsaw, Poland; †Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44-52, 01-224 Warsaw, Poland; and ‡Division of Biophysics, Institute of Experimental Physics, Department of Physics, University of Warsaw, al. Z ˙ wirki i Wigury 93, 02-089 Warsaw, Poland Received April 17, 2001 Although -nucleosides are not found in nucleic acid, they do occur as constituents of smaller molecules in living cells, e.g., in vitamin B 12 . There are now several examples of -nucleosides exerting a biological activity in some instances equal to, or even exceeding, that of the corresponding -anomer. Examples include growth in- hibitory properties against mouse leukemia cells and antitumor activity. From stereochemical point of view, -anomers serve as references for studying of interac- tion of the base with the sugar moiety in -anomers and may help in better understanding of structure–activity relationships. One important problem preventing con- formational analysis of  nucleosides is uncertainty in the determination of vicinal coupling constants from simulation of overlapping sugar proton resonances of strongly coupled spin systems. A successful resolution of near-isochronous H3 and H4 resonances made possible a full conformational analysis for a series of -anomers C5-substituted 2-deoxyuridines, including methyl, ethyl, isopropyl, fluor, vinyl, and bromovinyl, in compar- ison to their  counterparts. Conformation of the sugar ring is determined from proton–proton coupling con- stants and described in terms of pseudorotation be- tween two main puckering domains C2endo (S) and C3endo (N). A thorough analysis of chemical shifts as well as conformation of the sugar ring and C4–C5 rota- mers made possible determination of conformational preferences in equilibrium about the glycosidic bond between two regions, anti and syn. This work provides insights into the role of anomeric configuration of the base in conformational behavior of the sugar moiety, a link in the backbone of nucleic acids. © 2001 Academic Press Although -nucleosides are not found in nucleic acid, they do occur as constituents of smaller molecules in living cells e.g., -adenosine was found in the corrinoid factor from Propionobacterium shermanii (1), 1-(2,3- dideoxy--L-glyceropentopyranosyl)-cytosine and 1-(3- deoxy--L-threo-pentopyranosyl)-cytosine were isolated from culture filtrates of Streptomyces gryseochromogens (2), -benzimidazole ribonucleoside is a constituent of the vitamin B 12 (3), and -nicotinamide adenine dinucleotide phosphate was found in Azobacter vinelandi (4). There are now several examples of -nucleosides exerting bio- logical activity in some instances equal to, or even exceed- ing, that of the corresponding -anomer. First it was found that -anomers of 2-chloro- and 2-methoxy-2'- deoxyadenosine exhibit appreciable activity against murine leukemia L1210 (5), but the most instructive example is the antitumor activity of -anomer of 6-thioguanine-2'-deoxyriboside. This compound exhibit- ing lower toxicity against bone marrow than the corre- sponding -anomer, permits the use of higher concentra- tion with accompanying higher efficacy (6). More recently Bretner et al. (7, 8) observed that -anomers of 2'-deoxy-5-fluoro-2-thiouridine and cyti- dine exert selective (in comparison to 3T3 cells) growth inhibitory properties against L1210 and L5178Y mouse leukemia cells. -Nucleosides are substrates/ inhibitors in various enzymatic systems. 5-Formyl-1- (-D-ribofuranosyl)uracil readily undergoes intracellu- lar phosphorylation to its 5'-triphosphate, which prove to be an inhibitor of E. coli DNA polymerase (9), -5- ethyl-2'-deoxycytidine is a substrate of wheat shoot phosphotransferase (10), -2'-deoxythymidine is a good substrate of human thymidine kinases TK1 and TK2, and 3'-branched -L- and -D-deoxycytidines proved to be good substrates of human deoxycytidine 1 To whom correspondence should be addressed. Fax: 48-22-822- 0248. E-mail: remin@biogeo.uw.edu.pl. Biochemical and Biophysical Research Communications 283, 1142–1149 (2001) doi:10.1006/bbrc.2001.4921, available online at http://www.idealibrary.com on 1142 0006-291X/01 $35.00 Copyright © 2001 by Academic Press All rights of reproduction in any form reserved.