Raman spectroscopic determination of thymidine nucleoside structures in nucleotides
Several spectral differences in Raman spectra were observed for thymidine (TM), 3′-O-acetylthymidine (3′OATM), 3′,5′-di-O-acetylthymidine (3′5′DOATM), thymidine 5′-monophosphoric acid (H2TMP) and its Ca2+, Sr2+ and Ba2+ salts owing to nucleoside conformational differences in the thymidine moiety. The spectroscopic characterization of the nucleoside structures was made on the basis of previous crystallographic works relative to TM, 3′OATM, 3′5′DOATM and Ba(TMP)·6H2O. The crystal structures of the other compounds reported here are, as yet, unknown. However, their nucleoside structures were inferred from the position of the phosphoester stretching band. The results show that C(2′)-endo-anti, C(3′)-endo-anti and C(2′)-endo/C(3′)-exo-anti puckers generate marker bands useful to characterize and titrate these thymidine nucleoside conformations. The furanose sugar puckering of the C(2′)-endo-anti geometry has been suggested to account for the enhanced activity of thymidine derivatives against human immunodeficiency virus-type 1. A Raman spectroscopic method is described for the determination of this structure in thymidine nucleosides and nucleotides.