Six new photolabile linkers for solid phase synthesis. 2. Coupling of various building blocks and photolytic cleavage

Photolabile linkers are very useful in the generation of combinatorial libraries as they offer compound cleavage under mild conditions directly into a solvent suitable for biological testing. Six new photolabile linkers have been developed which allow coupling of building blocks with a carboxy, amino, hydroxy and sulfonyl group. Photolytic cleavage of these building blocks will give libraries with carboxy, amido, methylamido, amino, ureido, hydroxy, aminocarbonyloxy and aminosulfonyl terminal groups. Coupling conditions for these reactions were elucidated and the photolytic cleavage reaction was studied.     

Studies on chymotrypsin-like catalysis by synthetic peptides

The synthetic peptide Chymohelizyme-1 (CHZ-1) exhibits esterase activity against carbobenzoxytyrosinep-nitrophenyl ester (ZTONP), carbobenzoxyalaninep-nitrophenyl ester (ZAONP), andt-butyloxycarbonyltyrosinep-nitrophenyl ester (BocTONP). However, earlier reports of catalytic activity against less labile esters and amides have proven to be incorrect. The major reason for the errors appears to have been the omission of certain controls in the previous work. Although the catalytic triad does not appear to be functioning as designed, the catalytic activity of CHZ-1 does depend on the integrity of its primary structure. The pH dependence of hydrolysis of ZTONP points to general-base catalysis, whereas a preference for hydrophobic substrates suggest that the structure of CHZ-1 is performing some other role in assisting catalysis.     

On finite matroids with one more hyperplane than points

In this paper a complete classification of finite matroids with one more hyperplane than points is obtained.Dedicated to Professor Maria Scafati Tallini on the occasion of her 65th birthday     

Glycosylidene Carbenes. Part 16. Glycosidation of methyl 6-O-trityl-α-D-altropyranoside

Hydrogen bonding of the triol 4 in chlorinated solvents was studied by IR (CH₂Cl₂ and CCl₄) and ¹H-NMR spectroscopy (CDCl₃), and the regioselectivity of the glycosidation of the triol 4 by the diazirine 1 is predicted on the basis of two assumptions: preferred protonation of the intermediate glycosylidene carbene by the OH group involved in the weakest intramolecular H-bond, and attack in the π-plane of the thereby generated oxycarbenium cation either by the reoriented oxy anion, or by a properly oriented vicinal OH group. Glycosidation led to the disaccharides 5–10 (Scheme) which were separated and characterized as their acetates 11–16 , to the lactone azines 17 and to the 2-(benzyloxy)glucal 18 . In agreement with the predictions, glycosidation in non-coordinating solvents gave the 1,2-, 1,3-, and 1,4-linked disaccharides in decreasing relative amounts. Glycosidation in THF proceeded with a lower degree of regioselectivity and led preferentially to the β -D -anomers, except for the minor, 1,4-linked disaccharides, where THF had only a weak influence on stereoselectivity at room temperature and led to a slight increase of the α -D -anomer at ?80°.