Shigella flexneri serotypes 1b and 1a are Gram-negative enteroinvasive bacteria causing shigellosis in humans. The O-antigen from S. flexneri 1b is a { → 2)-[3Ac/4Ac]-α-L-RHAP-(1 → 2)-α-L-Rhap-(1 → 3)-[2Ac]-α-L-Rhap-(1 → 3)-[α-D-Glcp-(1 → 4)]-β-D-GlcpNAc-(1 → }n branched polysaccharide ({(Ac)AB(Ac)C(E)D}n). It is identical to that from S. flexneri 1a, except for the 2C-acetate. A concise synthe...

The aryl-(Z)-N-[2-amino-1,2-dicyanovinyl]formamidine 2 cyclize in solvent-free conditions and in the presence of a base to give a 5-amino-1-aryl-4-cyanoimidazoles 3. Silica sulfuric acid as an efficient and reusable heterogeneous catalyst has been used for the preparation of amidines 2 from formimidate 1 through reaction with aromatic amines at room temperature and in good to excellent yields. ...

The aryl-(Z)-N-[2-amino-1,2-dicyanovinyl]formamidine 2 cyclize in solvent-free conditions and in the presence of a base to give a 5-amino-1-aryl-4-cyanoimidazoles 3. Silica sulfuric acid as an efficient and reusable heterogeneous catalyst has been used for the preparation of amidines 2 from formimidate 1 through reaction with aromatic amines at room temperature and in good to excellent yields. ...

Asymmetric catalytic transfer hydrogenation using 2-propanol as a hydrogen source offers an attractive route for reducing simple unfunctionalized ketones to chiral alcohols.1 The reaction uses inexpensive reagents and is usually easy to perform. Notable among the recently developed efficient transition-metal-based chiral reduction catalysts2 is the Ru(II)-TsDPEN (TsDPEN ) N-(p-tolylsulfonyl)-1,...

A variety of C-disaccharides have been selectively and expeditiously synthesized through the so-called tether approach. Jntroduction . 'Oligosacch&ides are involved in a increasing number of biological processes. This has stimulated the development of selective methods for the synthesis of such complex molecules. Among others, the imidate. procedure that we have discovered (ref. l), and which h...

A new stereoelectronic theory for the cleavage of the tetrahedral intermediate in the hydrolysis of esters and amides is presented. In this new theory, the precise conformation of the intermediate hemi-orthoester or hemi-orthoamide controls the nature of the hydrolysis products. It is postulated that the breakdown of a conformer of a tetrahedral intermediate depends upon the orientation of the ...

Since the isolation of potent cytotoxic communesins A and B from a marine fungal strain of Penicillium sp. in 1993,1 eight members (A-H) of this structurally intriguing indole alkaloid family were consecutively disclosed over the past 5 years2 (Figure 1). Although the polycyclic framework and multiple stereocenters of communesins have attracted intensive synthetic efforts toward skeletal constr...