Carbon-13 Nuclear-Magnetic-Resonance Spectra of Adenine Cyclonucleosides and Their Phosphates. Effects of Neighboring Groups for Elucidation of Fine Structure of Nucleosides and Nucleotides

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Abstract
13C NMR spectra of adenine cyclonucleosides, which have a fixed glycosidic conformation in an anti range, and their isopropylidene and phosphate esters are reported; those of 9-.beta.-D-arabinofuranosyladenine and its 5''-phosphate are also presented. The chemical shifts of the base C are affected not only by the bridging atom but also by the position of the bridged sugar C which determine the planarity of the 3rd ring formed by cyclization between the base and the sugar. The effects of glycosidic conformation on the sugar-C chemical shifts are discussed in comparison with the data for 8:5''-cycloadenosines with the data for adenosine and its 8-substituted derivatives. The effects of a 2''-O on sugar-C chemical shifts were examined by comparing the data for 2''-deoxyadenosine, arabinosyladenine and 8:2''-anhydro-8-oxy-9-.beta.-D-arabinofuranosyladenine. The effects of phosphomonoester groups on base and sugar C resonances were examined. These groups cause downfield shifts for C-8 of all cyclonucleotides. Data for the 3'':5''-cyclic monophosphate derivative of 8:2''-anhydro-8-thio-9-.beta.-D-arabinofuranosyl-adenine suggest that the previous assignments of C-4'' and C-3'' for nucleoside 3'':5''-cyclic monophosphates must be reversed. According to the reversed assignments, it seems that C-3'' and C-5'' show moderate downfield shifts and C-4'' shows a marked upfield shift.

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