| Popis: |
Three new withanolides (C 28 steroids possessing a 6-membered ring lactone in the side chain) have been isolated from Withania somnifera (Solanaceae) growing in South Africa and characterized as 4β-hydroxy-1-oxo-5β,6β-epoxywitha-2,24-dienolide (IIIa), 4β,20α,( R )dihydroxy-1-oxo-5β,6β-epoxywith-2-enolide (IVa), and 4β-hydroxy-1-oxo-5β,6β-epoxywith-2-enolide (Va). The major steroidal components of the above plant are the known withaferin A (4β,27-dihydroxy-1-oxo-5β,6β-epoxywitha-2,24-dienolide) and withanolide D (4β,20α,( R )-dihydroxy-1-oxo-5β,6β-epoxywitha-2,24-dienolide). The structures assigned to compounds IIIa, IVa and Va are based on spectral evidence (NMR, IR and UV), analysis of their fragmentation under electron impact, as well as on chemical degradation to known compounds. |
