Current Organic Chemistry - Volume 9, Issue 14, 2005

The data concerning the structure, synthesis and reactivity of six-membered ring spiranes exhibiting carbocycles and heterocycles with oxygen atoms are reviewed. The structural aspects are discussed using specific stereogenic elements and stereochemistry descriptors for spiranes with six-membered rings. The data are supported by high field NMR investigations and molecular structures obtained by X-ray diffractometry. The general procedures and access to spiranes with carbocycles and with heterocycles with oxygen are commented.

Addition reactions to imines are relatively less developed compared to those of carbonyl compounds due to low electrophilicity and ease of α-deprotonation. With the use of an appropriate activator, which can coordinate to the imine nitrogen atom, the electrophilicity of the imine can be enhanced and a range of nucleophilic addition reactions becomes possible. When the activator is chiral, it will also create chiral environment and will direct the approach of the nucleophile to one face of the imine over the other resulting in enantioselectivity. The potential of catalytic asymmetric addition to imines in organic synthesis is enormous, but is relatively underused. With the development of many highly effective chiral catalysts for imine additions, the situation will soon be changed. The present review will cover selected literature on catalytic asymmetric additions to aldimines, ketimines and related compounds including hydrazones, oximes and nitrones from 1999 to 2004. The reactions of interest include hydrogenation, alkylation, Mannich and related reactions such as aza-Baylis-Hillman and aza-Henry reaction, Strecker reaction, hydrophosphonylation, and 3-6 membered ring forming reactions from imines. Some applications of these methodologies in synthesis of nitrogen-containing biologically active compounds will also be presented.

This review reports on recent developments on the structure, biological activities and synthesis of 3- hydroxylpyrrolizidine alkaloids and related compounds.

The chemical and biological properties of anti-inflammatory marine natural products whose mechanism of action involves inhibition of phospholipase A2 (PLA2), an enzyme of key importance in the biosynthesis of proinflammatory chemical signals and mediators, has been reviewed. Remarkably, most marine natural products display a selective inhibition profile against secretory PLA2 enzymes, with little or null ability to interfere with cytosolic PLA2. Variabilin, a marine furano-terpene, appears to be a notable exception, endowed with a distinctive dual inhibitor profile towards both secretory and cytosolic PLA2 proteins.