ene-4-C-hydroxymethyl-alpha-L-lyxofuranosyl)uracil (I) was converted i
n seven steps into -hydroxymethyl-alpha-L-threo-pentofuranosyl)uracil
(8) and further into isoprapylidene-alpha-L-threo-pentofuranosyl)uraci
l (9). Successive benzoylation, removal of the isopropylidene group, r
eaction with acetaldehyde diethyl acetal, and debenzoylation afforded
(R)- and -hydroxymethyl-alpha-L-threo-pentofuranosyl)uracil (10a and 1
0b, respectively). Reaction of ethyloxymethyl-alpha-L-threo-pentofuran
osyl)uracil (14) with dichloromethane under conditions of phase transf
er, followed by detritylation, afforded -O-methylidene-alpha-L-threo-p
entofuranosyl)uracil (15). Compound 14 was obtained from the derivativ
e 8 by partial silylation, tritylation and desilylation. The absolute
configuration of the isomeric ethylidene derivatives 10a and 10b was d
etermined by NMR spectroscopy and the population of the deoxypentofura
nose ring conformers was derived from the vicinal coupling constants I
(H,H). The obtained results were compared with energy calculations. Ne
ither of the prepared nucleoside analogues was active in vitro against
HIV-I and HIV-2.