MODIFIED NUCLEOSIDE STRUCTURE FUNCTION RELATIONS TRNA

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The biosynthesis of two cell-wall polymers, arabinogalactan and lipoarabinomannan, is to be studied with cell-free preparations of Mycobacterium smegmatis and M. Tuberculosis H37Ra. In the present phase of the project, chemical synthesis is being used to obtain nucleoside diphosphate derivatives of the pentose D-arabinose. The object is to test these derivatives as primary donors of D-arabinose residues in the biosynthetic process. The preferred synthetic procedure involves the glycosidation of D-arabinose to methyl a-D-arabinofuranoside, benzoylation of the glycoside to the 2,3,5-tribenzoate, and conversion of the benzoate into the protected glycosyl chloride and/or bromide. The glycosyl halides will then be treated with the tetrabutylammonium salts of uridine diphospate and guanosine diphosphate d-arabinofuranoses. Alternatively, tetrabutylammonium dibenzyl phosphate may be reacted with the protected arabinosyl chloride or bromide, and the product deprotected to give D-arabinofuranose 1-phosphate. Reaction of the 1-phosphate with the phosphormorpholidates of the nucleoside diphosphate of interest should give the corresponding nucleoside diphosphate arabinofuranoses. Since all or nearly all of the intermediates in the proposed syntheses, and two of the final products, have been described in the literature, operations can be monitored by examining the high resolution 1H NMR spectrum of each compound as it is obtained. For the final products 13C and 31P spectra may also be useful. Once the reliability of the syntheses is established with ordinary reagents, the preparation of radioactive samples will be undertaken, with 1-[14C]-D-arabinose as the labeled starting material.