Stereochemistry determination by NMR Residual Dipolar Couplings: application in natural products?

MANUELA E. GARCIA ; SILVINA PAGOLA; ARMANDO NAVARRO-VÁZQUEZ; MANUELA E. GARCIA, SILVINA PAGOLA, ARMANDO NAVARRO-VÁZQUEZ, DAMILOLA D. PHILLIPS, CHAKICHERLA GAYATHRI, HENRY KRAKAUER, PETER W. STEPHENS, VIVIANA E. NICOTRA AND ROBERTO R. GIL.; CHAKICHERLA GAYATHRI; VIVIANA E. NICOTRA ; ROBERTO R. GIL.

Golden, Colorado School of Mines. Estados Unidos

Otro; 8th Summer School on Green Chemistry and Sustainable Energy; 2010

American Chemical Society

The withanolides are a group of naturally occurring C28 steroids which are built on an ergostane skeleton functionalized at carbons 1, 22, and 26, and have a high occurrence in genera of the Solanacea family. In the present work we show the power of Nuclear Magnetic Resonance (NMR) Residual Dipolar Couplings (RDCs) on the determination of the absolute stereochemistry of six new steroidal lactones (withanolides) from Jaborosa parviflora. The final absolute stereochemistry of these compounds is determined relative to the established absolute configuration of the steroidal skeleton. The use of only conventional NMR spectroscopy experiments (NOE and 3J analysis) led to three ambiguous solutions for the structure of w. Without the aid of RDCs it would have posed great difficulty to complete the phytochemical study of Jaborosa parviflora and to unambiguously determine the stereochemistry of its isolates.