An unusual diepoxyguaianolide from Stevia tomentosa

Recent advances in the use of vibrational chiroptical spectroscopic methods for stereochemical characterization of natural products

“…113 The absolute conguration of the unusual diepoxyguaianolide (À)-63, isolated from Stevia tomentosa, was determined as 1S,3S,4S,5R,7R,8R,11S by VCD in combination with DFT (B3LYP/DGDZVP) calculations. 114 This assignment was supported by X-ray crystallography. The cassane diterpenes (À)-6-acetoxyvoucapane (64) (75), isolated from the endangered species Solidago shortii, was determined as 3R,4S,5R,7S,8S,9S,10S using VCD and DFT [B3LYP/6-311+G(2d,p)] calculations, as the crystal structure obtained for 75 did not allow for such assignment.…”

“…113 The absolute conguration of the unusual diepoxyguaianolide (À)-63, isolated from Stevia tomentosa, was determined as 1S,3S,4S,5R,7R,8R,11S by VCD in combination with DFT (B3LYP/DGDZVP) calculations. 114 This assignment was supported by X-ray crystallography. The cassane diterpenes (À)-6-acetoxyvoucapane (64), (À)-hydroxyvoucapane (65), and (+)-6-oxovoucapane (66), isolated from Caesalpinia platyloba, had their absolute congurations assigned as (5S,6R,8S,9S,10R,14R)-64, (5S,6R,8S,9S,10R,14R)-65 and (5S,8S,9S,10R,14R)-66 using VCD and DFT (B3LYP/ DGDZVP) calculations.…”

“…The novel compound (À)-111 was determined as 2R,3S,5S with the aid of calculations at the B3PW91/TZVP level. Compounds (À)-gnemonoside C (113) and (À)-gnemonoside D (114) were assigned as 7aS,8aS. 141 Several dimeric stilbene glucosides were isolated from Gnetum africanum and had their absolute congurations assigned using VCD and DFT [B3PW91/6-31G(d,p)] calculations.…”

Stevia Genus: Phytochemistry and Biological Activities Update

“…The new sesquiterpene lactone 1,5:3,4-diepoxyguaia-10(14)-en-12,8-olide ( 26 ) was described by Valdez-Calderón et al [ 23 ]. This diepoxyguaianolide, isolated from the aerial parts of S. tomentosa , contains two β-oriented epoxide groups in the five-membered carbocyclic ring.…”

Diastereoselective Addition of Diazomethane to Zaluzanin A

“…Table 2 contains the thermochemical analysis for the calculation of the conformational equilibrium of 2 which included the three main species 2a, 2b and 2c. The Boltzmann distribution was calculated according to the ΔG = ΔH -TΔS and ΔG = -RT ln K equations, considering the B3LYP/DGDZVP calculated frequencies, as recently described for a diepoxyguaianolide [12].…”