CONFORMATION OF 4-THIO-L-LYXONO-1,4-LACTONE IN SOLUTION AND IN THE CRYSTALLINE STATE

The conformation in (H2O)-H-2 of 4-thio-L-lyxono-1,4-lactone (1) was s tudied by nuclear magnetic resonance spectroscopy, by means of homonuc lear (J(1H,1H)) and heteronuclear (J(1H,13C)) coupling constants. The couplings were directly measured by a two-dimensional heteronucleus-co upled omega(1) hetero-half-filtered proton-proton correlation (HETLOC) experiment, which does not require C-13 isotopic enrichment. In solut ion, the thiolactone ring of 1 adopts preferentially the E(3) conforma tion, and its hydroxymethyl group populates mainly the gt rotamer. The X-ray diffraction data of a single crystal of 1 indicates that also i n the solid state the thiolactone ring adopts an E(3) conformation, wi th a puckering somewhat larger than that observed for aldono-1,4-lacto nes and furanose rings. The molecules are linked by hydrogen bonds, wh ich form chains. Particularly, O-5 is fully engaged as donor and accep tor in hydrogen bonding and the rotameric conformation of the hydroxym ethyl group of 1 is fixed in the tg form.