B.Lucas Sondengam

Entilins A and B, two novel heptanortriterpenoid derivatives from entandrophragma utile (meliaceae): Structural elucidation using 2d nmr long-range δC/δH correlation experiments

Entilin A and its 2-acetate, entilin B, isolated from the stem bark of Entandrophragma utile have been assigned structures 1 and 2 mainly by using deductive arguments to interpret 2D NMR long-range δC/δH correlation experiments.

The structures of vepridimerines A-D, four new dimeric prenylated quinolone alkaloids from Vepris lousii and Oricia renieri (Rutaceae)

Abstract Four new isomeric dimeric prenylated quinolone alkaloids, vepridimerines A-D, have been isolated from the bark of Vepris louisii and Oricia renieri (Rutaceae) and have been assigned structures (2)–(5) respectively on the basis of spectroscopic evidence, in particular 1 H and 13 C n.m.r. data.

The use of two-dimensional long-range δC/δH correlation in conjunction with the one-dimensional proton-coupled 13C NMR spectrum in the structural elucidation of ekeberginine, a new carbazole alkaloid from Ekebergia senegalensis (Meliaceae)

A new strategy involving the use of 2D long-range δC/δH correlation in conjunction with the 1D proton-coupled 13C NMR spectrum has been applied to the structural elucidation of ekeberginine, a new carbazole alkaloid from the stem bark of Ekebergia senegalensis (Meliaceae).

Pachypophyllin and pachypostaudins A and B: three Bisnorlignans from Pachypodanthium staudtii

Abstract Three new bisnor lignans, pachypophyllin, pachypostaudin-A and pachypostaudin-B have been isolated from the bark of Pachypodanthium staudtii and their structures have been determined by 1 H and 13 CNMR spectroscopy and chemical correlations. 2,4,5-Trimethoxystyrene, probably a precursor of the bisnor lignans, was also isolated from the extracts. Furthermore, the potent antiviral flavonol, pachypodol, was obtained in significant amount.

Veprisine and N-methylpreskimmianine: Novel 2-quinolones from Vepris louisii

Abstract The structures of two new 2-quinolone alkaloids, N-methylpreskimmianine and veprisine (7,8-dimethoxy-N-methylflindersine) have been deduced from their spectra and confirmed by partial synthesis from known compounds.

Cecropiacic acid, a new pentacyclic A-ring seco triterpenoid from Musanga cecropioides

Abstract From the methylated polar extract of stem bark of Musanga cecropioides (Cecropiaceae) a novel triterpenic A-ring seco derivative has been obtained and the structure elucidated by spectroscopic methods.

Partially-acetylated dodecanyl tri- and tetra-rhamnoside derivatives from Cleistopholis glauca (annonaceae)

Abstract Five partially-acetylated derivatives (1)-(5) of 1- o -dodecanyl α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→4)-α-L-rhamnopyranoside have been isolated from the bark of Cleistopholis glauca (Annonaceae) and their structures elucidated by using COSY, delayed COSY, and FAB Mass spectroscopy. The trisaccharide 1- o -dodecanyl α-L-2,3,4-triacetylrhamnopyranosyl-(1→3)-α-L-4-acetylrhamno-pyranosyl-(1→4)-α-L-rhamnopyranoside (6) was also isolated.

Synthesis of Veprisine Dimers and the Formation of a Novel Cyclic Tetramer from Precocene I

Thermolysis of veprisine afforded vepridimerines A–D and in addition, a new dimer, vepridimerine E. The full details of the 1H and 13C NMR spectroscopic properties of vepridimerines A–E are presented. Acid treatment of veprisine gave another new dimer, diveprisine, analogous to the known precocene II dimer. Under the same conditions precocene I was transformed into a cyclic tetramer. High field NMR examination of the coumarin dimer, reported by Barnes et al. in 1963, confirmed the assigned structure.

Oriciopsin, a new ring-D cleaved tetranortriterpenoid, and flindersiamine from Oriciopsis glaberrima

Abstract A novel ring-D cleaved tetranortriterpenoid, oriciopsin and flindersiamine have been isolated from the whole plant extracts of Oriciopsis glaberrima . The structure of the new limonoid was determined from its 1 H NMR and 13 C NMR spectra and by mass spectrometry.

Veprisilone, a prenylated 2-quinolone, and limonin from Vepris louisii

Abstract A new 2-quinolone alkaloid, veprisilone, isolated from the trunk bark of Vepris louisii has been characterized as 3-(3-hydroxy-3-methyl-2-oxobutyl)- 4,7,8-trimethoxy-1-methyl-2-quinolone from spectral and chemical data. Limonin was also identified in the extracts.