ABSTRACT
An unprecedented macrocyclic dimeric diterpene containing a C2 symmetry axis was isolated from Acacia schaffneri . This compound, named schaffnerine, was characterized as (5S,7S,8R,9R,10S,17S,5'S,7'S,8'R,9'R,10'S,17'S)-7,8:7,17':16,17:17,7':7',8':16',17'-hexaepoxy-7,8-seco-7',8'-seco-dicassa-13,13'-diene (1) from its spectroscopic data. Comparison of its experimental vibrational circular dichroism spectrum with that calculated using density functional theory, at the B3LYP/DGDZVP level, assigned its preferred conformation and absolute configuration. The latter was confirmed by evaluation of the Flack and Hooft parameters obtained after single-crystal X-ray diffraction analysis.
Subject(s)
Acacia/chemistry , Diterpenes/isolation & purification , Circular Dichroism , Crystallography, X-Ray , Diterpenes/chemistry , Models, Molecular , Molecular Conformation , Molecular Structure , StereoisomerismABSTRACT
The new sesquiterpene (1R,2R,3R,6R,7S)-1-acetoxy-2,3-dihydroxy-2,3-dihydrobisabolene (3) together with ten known terpenes and three known flavonoids were isolated from the aerial parts and from the roots of Stevia tomentosa. The structure of 3 follows from spectral studies, the relative chirality at C-3 follows from 1H NMR coupling constants comparison with the corresponding calculated values obtained by applying a generalized Karplus-type relationship to the dihedral angles of model compounds, and the absolute configuration is assumed in analogy to known (2R,3R,6R,7S)-2,3-epoxy-2,3-dihydrobisabolen-1-one (2).
Subject(s)
Sesquiterpenes/chemistry , Stevia/chemistry , Molecular Structure , Plant Components, Aerial/chemistry , Plant Roots/chemistryABSTRACT
The ethanol extract from the dried exudate of Bursera fagaroides (Burseraceae) showed significant cytotoxic activity in the HT-29 (human colon adenocarcinoma) test system. The extract provided four podophyllotoxin related lignans, identified as (7'R,8R,8'R)-(-)-deoxypodophyllotoxin (3), (7'R,8R,8'R)-(-)-morelensin (4), (8R,8'R)-(-)-yatein (5), and (8R,8'R)-(-)-5'-desmethoxyyatein (6), whose spectroscopic and chiroptical properties were compared with those of (7R,7'R,8R,8'R)-(-)-podophyllotoxin (1) and its acetyl derivative (2). Their absolute configurations were assigned by comparison of the vibrational circular dichroism spectra of 1 and 3 with those obtained by density functional theory calculations.
