BASE-HYDROGENATED PHOSPHONIC ACID-DERIVAT IVES OF PYRIMIDINE NUCLEOSIDES, SIDE PRODUCTS IN THE DEOXYGENATION OF 2'-O-PHENOXYTHIOCARBONYL PRECURSORS

Persilylation of phenoxythiocarbonyl-beta-D-ribofuranosyl)cystosine (1 ) with iodotrimethylsilane followed by a Barton-McCombie reaction with Bu3SnH/azobis(isobutyronitrile) and hydrolysis with Et3NH+ buffer fur nishes, in a side reaction, the oxy-3'-phosphonomethyl-3,4,5,6-tetrahy dro-cytosine lactones 4a and 4b, which are epimers at C-4 and can be s eparated by chromatography, Two-step hydrolysis of 4a and/or 4b yields an epimeric mixture of l-beta-D-ribofuranosyl)-3,4,5,6-tetrahydro-ura cil. A possible mechanism of the formation of 4a/4b from 1 via persily lated iethoxyphosphoryl-beta-D-arabinofuranosyl)cytosine (9) as well a s the reactivity of 9 and the behaviour of methyl phenoxythiocarbonyl- beta-D-erythro-pentofurdnoside (17) under the same reaction conditions are discussed. The structures of all new compounds are confirmed by t heir H-1, C-13, P-31-NMR and FAB mass spectra.