Synthèse de l'apiose et de composés voisins par des réactions de wittig

Treatment of 1,2-O-isopropylidene-α-D-glycero-tetros-3-ulofuranose (7) with cyanomethylenetriphenylphosphorane gave in excellent yield a mixture of the geometrical isomers of the corresponding cyanomethylenic derivative. After treatment with potassium permanganate, and then with sodium borohydride, this unsaturated, branched-chain sugar derivative was stereospecifically converted into 3-C-hydroxymethy]-1,2-O-isopropylidene-β-L-threofuranose. Similarly, treatment of the L-enantiomer of 7 with methylthiomethylenetriphenylphosphorane gave the expected methylthiomethylenic analogs, from which 3-deoxy-3-C-methyl and 3-deoxy-3-C-dimethoxymethyl derivatives were prepared. Wittig reactions thus allow the synthesis of branched-chain sugars bearing the side-chain on the more hindered side of the ring, compounds which are difficult to obtain by other methods.     

Équilibres conformationnels de glucides au niveau de liaisons σ SP-SP: Partie V. Dérivés 2,3,-O-isopropylidène de pyranosides hybrides sp en C-4. Comparaison avec leurs analogues saturés

The conformation in solution of derivatives of methyl hexopyranosides has been studied by n.m.r. The esters of methyl 2,3-O-isopropylidene-α-D-manno- and -talopyranosides as well as their 4-deoxy-4-C-methyl analog having a manno configuration exist mainly in a flattened (^4,0F) chair conformation (⁴C₁). The presence in the talo epimer of the 4-deoxy-4-C-methyl analog of the bulky methyl group on the endo side of the bicyclic system results in a skew form (³S₁). The methyl 4-deoxy-2,3-O-isopropylidene-4-C-methylene-α-D-lyxo-hexopyranosides monosubstituted at C-4′ adopt, in solution, a conformation close to ³S₁, whichever their configuration (cis or trans) at the double bond, as indicated by their allylic coupling constants.     

Dérives C-glycosyliques : XIII. Nitrones de sucres

Various N-methylnitrones of sugars having a free carbonyl group were prepared by treatment with N-methylhydroxylamine. In each case, only one geometric isomer was obtained, to which the anti (Z) configuration is ascribed on the basis of the n.m.r. spectra, in particular of those obtained in the presence of an europium complex.     

Mise en Evidence de la Carcinine Synthétase, une Nouvelle Enzyme Catalysant le Métabolisme de l''Histamine dans le Systeme Nerveux Central de Carcinus maenas

Carcinine biosynthesis was induced in vitro from its two components, beta-alanine and histamine. The reaction was catalyzed by muscle, heart, and CNS extracts from Carcinus maenas. The specific activity of the enzyme, carcinine synthetase, was 15 times higher in CNS than in other organs. Only CNS extracts induced biosynthesis of carcinine from histidine, and only in the presence of pyridoxal-5'-phosphate. Hence the seat of carcinine biosynthesis seems to be the CNS. It is highly probable that in the CNS, histidine is transformed into histamine, which is then catabolized into carcinine. The latter would then be transported and accumulated in the cardiac tissue. Thus histamine--the metabolism of which takes place totally within the CNS--would be implicated as a participant in the neuronal activity of Carcinus maenas. Carcinine synthetase is a soluble enzyme that requires the presence of ATP, beta-alanine, and histamine. Mg2+ and dithiothreitol are also essential for activity. Optimum pH is approximately 7.6. Carcinine synthetase differs from carnosine synthetase and gamma-glutamylhistamine synthetase in that it does not catalyze synthesis of beta-alanylhistidine or gamma-glutamylhistamine.