Determination of the Relative Configurations in the Side Chains of the Antibiotics Hedamycin and Pluramycin A; Synthesis and NMR. Data of Suitable Model Compounds

Total Synthesis and Structure Assignment of Saptomycin H

We report herein the first total synthesis of saptomycin H (2), by which the unidentified absolute stereochemistry of the oxiranyl side chain has been determined as 14R,16S. The keys include (1) concise assembly of three units, anthrone, sugar and side chain, and (2) AZADOL-mediated 6-endo-selective pyranone (A-ring) formation.

Diastereoselective One-Step Synthesis of Functionalized cis-Aziridinyl Alcohols from Oxiranyl Carbaldimines

[reaction: see text]. Upon treatment with lithiumorganic nucleophiles, trans-configured oxiranyl carbaldimines are transformed into anti-configured cis-aziridinyl alcohols with excellent diastereoselectivity. This conversion may be explained by a new type of the aza-Payne rearrangement, including first a nucleophilic attack on the imine carbon atom with diastereofacial differentiation followed by an intramolecular nucleophilic opening of the oxiranyl ring with simultaneous formation of the aziridine ring.

Eight new prenylcoumarins from Phebalium clavatum

The aerial parts of Phebalium clavatum yielded eight new 3-prenylated coumarins, phebaclavin A-H (1-8). Their structures were established on the basis of their NMR and mass spectral data. In addition, seven known compounds were also isolated, including two 8-geranyloxy linear furocoumarins previously obtained from Phebalium tuberculosum ssp. megaphyllum, included in the same section of the genus.

Base-induced heterochiral dimerization of an oxiranyl carbaldimine: stereoselective synthesis of a highly functionalized aziridine

[reaction: see text] Treatment of the oxiranyl carbaldimine with base (LDA or LDA/KOtBu) leads in an one-step procedure to the polyfunctionalized aziridine. This highly diastereoselective reaction is explained by a new type of an Aza-Darzens reaction, in which one enantiomer of the starting material is deprotonated to form an oxiranyl anion, which attacks the imine carbon atom of the other enantiomer (mutual kinetic resolution by double diastereofacial selection).

Synthesis of C-glycopyranosyl compounds by a palladium-catalyzed coupling reaction of 1-tributylstannyl-D-glucals with organic halides

1-Tributylstannyl-D-glucals, prepared from the corresponding 1-phenylsulfonyl-D-glucals, were coupled efficiently to various organic halides in the presence of a palladium(0) catalyst. This mild reaction is specially useful for the preparation of 1-C-aryl-D-glucals and compatible with unprotected hydroxy groups or hindered aromatic bromides. It has been shown that the resulting 1-C-aryl(alkyl)-D-glucals are suited for further synthetic manipulation of the enol ether group, including stereoselective hydrogenation, hydroboration-oxidation, or epoxidation. All compounds formed resulted from the attack of the alpha-face of the glucal derivatives by the reagent. The reaction, extended to 1,3-, 1,4-di-, and 1,3,5-tri-bromobenzenes, leads to the corresponding symmetrical di-(tri)-C-glucosylbenzenes. Finally, a sequential di-C-glucosylation of 1,3-dibromobenzene with two different 1-stannylated glucals was obtained.