Synthesis of cyclopentane analogs of (2′- and 3′-deoxy-erythro-pentofuranosyl and ribofuranosyl)-2-thiouracil nucleosides

Three new carbocyclic analogs of nucleosides having the 2-thiouracil base have been synthesized. The cyclopentyl groups in these nucleosides are (±)-{(1β,3α,4β)-3-hydroxy-4-(hydroxyrnethyl)cyclopentyl} (see 31), (±)-{(1β,2α,4β)-2-hydroxy-4-(hydroxymethyl)cyclopentyl} (see 32), and (±)-{(1β,2α,3α,4β)-2,3-dihydroxy-4-(hydroxymethyl)cyclopentyl} (see 33). The nucleosides were prepared by coupling the appropriate hydroxy derivatives of cis-3-aminocyclopentanemethanol with 3-ethoxypropenoyl isothiocyanate (21) followed by cyclization in 15 N aqueous ammonia to give the 2-thiouracil nucleosides. In addition a modified and shortened synthetic route is described for the synthesis of (±)-(1β,2α,3α,4β)-4-amino-2,3-dihydroxy-cyclopentanemethanol (19). The 1H nmr spectra at 200 MHz of all of the synthetic intermediates, the 2-thiouracil nucleosides, and of the corresponding carbocyclic analogs of uracil nucleosides are discussed. It is shown that each nucleoside has a characteristically unique 1H nmr spectrum and that in general the protons in the sulfur-containing compounds resonate at lower fields than those in the corresponding oxygen-containing compounds. The magnitude of this downfield shift is inversely related to the number of bonds separating a particular proton from the sulfur atom.