Multistereocenter-Containing Cyclopentanoids from Ynamides via Oxazolidinone-Controlled Nazarov Cyclization.

Achieving ready-enantioselective access to multistereocenter-containing cyclopentyl rings is an area of great significance to organic synthesis. In this work, we describe a general protocol for accessing multistereocenter-containing cyclopentanoids from simple N-alkynyloxazolidinones (Ox-ynamides). This protocol involves conversion of Ox-ynamides into Ox-activated divinyl and aryl vinyl ketones that undergo facile Nazarov cyclization with excellent chemo-, regio-, and stereocontrol.

First Atroposelective Total Synthesis of Enantiomerically Pure Ancistrocladidine and Ancistrotectorine.

The first regio- and stereoselective total synthesis of the axially chiral 7,3'-coupled naphthylisoquinoline alkaloids ancistrocladidine (1) and ancistrotectorine (2) has been described. Both possess a 7,3'-coupled axis, which before now, was difficult to attain synthetically. Moreover, target 2 has a sensitive relative cis-array of the two methyl groups at C1 and C3 in the tetrahydroisoquinoline part.

Asymmetric synthesis of (+)- and (-)-pauciflorol F: confirmation of absolute stereochemistry.

An efficient, formal enantioselective synthesis of (+)- and (-)-pauciflorol F has been achieved using a recently introduced oxazolidinone controlled torquoselective Nazarov reaction. The absolute stereochemistry of pauciflorol F and its biosynthetic precursors has been unambiguously confirmed using X-ray crystallography.

Opposing auxiliary conformations produce the same torquoselectivity in an oxazolidinone-directed Nazarov cyclization.

Most applications of chiral oxazolidinone auxiliaries in asymmetric synthesis operate through a common set of stereocontrol principles. That is, the oxazolidinone is made to adopt a specific, coplanar conformation with respect to the prochiral substrate, and reaction occurs preferentially at whichever stereoheterotopic face is not blocked by the substituents on the oxazolidinone. In contrast to these principles, we report here the discovery of an alternative mechanism of oxazolidinone-based stereocontrol that does not require coplanarity and is driven instead by allylic strain.

Chemical examination of the Sponge Phycopsis sp.

Two new compounds 7alpha,8alpha-epoxy theonellin isothiocyanate (1) and 5alpha,8alpha-epidioxyergosta-6Z,22Z,25-trien-3beta-ol (2) along with two known compounds, theonellin isothiocyanate (3) and theonellin formamide (4) have been isolated from the sponge Phycopsis sp. Compound 2 showed cytotoxic activity against HL-60 and U937 human cancer cell lines with IC(50) values of 5.96+/-0.

Isolation, characterization and biological evaluation of bioactive metabolites from Nocardia levis MK-VL_113.

An Actinomycete isolate found to be prominent in the laterite soils of Acharya Nagarjuna University (ANU) Campus, Guntur was identified as Nocardia levis MK-VL_113 by 16S rRNA analysis. Cultural, morphological and physiological characteristics of the strain were recorded. Screening of secondary metabolites obtained from 4-day old culture broth of the strain led to the isolation of two fractions active against a wide variety of Gram-positive, Gram-negative bacteria and fungi.