7-Deazaxanthine (7DX) was identified as a novel inhibitor of thymidine (dThd) phosphorylase (TPase). It inhibited the TPase reaction in a concentration-dependent manner. At 1 mM, it almost completely prevented the TPase-catalysed hydrolysis of dThd to thymine. The 50% inhibitory concentration (IC SH ) of 7DX was 40 W WM in the presence of 100 W WM of the natural substrate dThd. 7DX is also endowed with a marked inhibitory effect on angiogenesis. It significantly prevents neovascularisation in the chicken chorioallantoic membrane during development. 7DX is the first purine derivative shown to be a potent inhibitor of purified TPase and angiogenesis.z 1998 Federation of European Biochemical Societies.

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.

The syntheses of enantiomerically pure (Z)-3-p-tolylsulfinylacrylonitrile (1b) and its 2-n-butyl (1a), 2-tert-butyl (1c), and 2-benzyl (1d) derivatives, by stereoselective hydrocyanation with Et 2 AlCN of their corresponding alkynylsulfoxides, are described. Asymmetric Diels-Alder reactions of these dienophiles with cyclopentadiene are also reported, the most significant finding being their total π-facial diastereoselectivity, controlled by the sulfur configuration, which can be readily inverted by using BF 3 as a catalyst. The endo selectivity is very high for 1b under thermal and catalytic (ZnBr 2 ) conditions and complete in the presence of BF 3 , whereas 1a and 1d only exhibit a complete endo selectivity in the presence of BF 3 .

Synthesis and Dienophilic Behavior of Enantiomerically Pure (Z)-3-p-Tolylsulfinylacrylonitriles.-Under thermal as well as catalytic ZnBr 2 conditions the title nitriles (IIIa)-(IIIc) react with the diene (IV) to afford the adducts (V) and (VI) with complete π-facial diastereoselectivity.In the presence of BF 3 ·OEt 2 the π-facial diastereoselectivity can be totally reversed. Interestingly, in the latter case exclusive formation of the endo-adducts (VII) takes place with concomitant inversion of the sulfur configuration. -(GARCIA RUANO, J. L.; ESTEBAN GAMBOA, A.; MARTIN CASTRO, A. M.; RODRIGUEZ, J. H.; LOPEZ-SOLERA, M. I.; J.

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines. -The Diels-Alder reaction of the new sulfilimine (IIa) proceeds with complete endo and π-facial selectivity. -(GARCIA RUANO, JOSE L.; ESTEBAN GAMBOA, ANTO-NIO; GONZALEZ GUTIERREZ, LORENA; MARTIN CASTRO, ANA M.; RODRIGUEZ RAMOS, JESUS H.; YUSTE, FRANCISCO;