Klaus-Peter Gulden

Circular dichroism of naphthyltetrahydroisoquinoline alkaloids: calculation of CD spectra by semiempirical methods

Abstract The circular dichroism (CD) of the naturally occurring biaryls ancistrocladine and hamatine - the most important representatives of naphthylisoquinoline alkaloids - has been studied. Semiempirical all valence electron calculations using the CNDO/2S method have been applied to reproduce the experimental CD spectra of the two alkaloids with known absolute configuration at the biaryl axis. Based upon the good agreement of experimental and calculated data, a more reliable assignment of axial chirality for so far undetermined structures of natural as well as synthetic compounds may be expected.

Circular dichroism of michellamines: Independent assignment of axial chirality by calculated and experimental CD spectra

Abstract The circular dichroic behavior of the michellamines, dimeric naphthylisoquinoline alkaloids, was investigated. Due to the molecular size and conformational flexibility, which makes direct calculations of the CD spectra very difficult, and because of the lack of direct standards for an empirical comparison, there is no simple possibility for the interpretation of the CD spectra of such quateraryls. The chiroptical contributions of the particular stereogenic elements were shown to behave largely additively and thus allow comparison of spectra of the quateraryls with those of the corresponding ‘monomeric’ naphthylisoquinolines. This comparison was performed first of all with the experimental and theoretical CD spectra of ancistrobrevine B, then with the predicted spectra of the authentic molecular ‘halves’ of the michellamines.

Gentrymine B1, the first quaternary isoquinoline alkaloid from Ancistrocladus korupensis

Abstract A novel tetrahydroisoquinoline alkaloid, gentrymine B ( 3 ), was isolated from the tropical liana Ancistrocladus korupensis . Although numerous naphthyl tetrahydroisoquinoline alkaloids have been found in the genus Ancistrocladus , no such quaternary alkaloid has previously been reported as a natural product.

Synthesis and absolute stereostructure of dinaphth[2,1- c: 1′,2′-e]oxepin-3-(5H)-one ☆

Abstract The synthesis, enantiomer analysis, and configurational assignment of dinaphth[2,1-c: 1′,2′-e]oxepin-3-(5H)-one, a seven-membered lactone-bridged chiral binaphthalene, is reported. The elucidation of the absolute configuration has been performed, independently by multiple scattering X-ray experiments and by circular dichroism (CD).

Calculation of circular dichroism spectra of michellamines A and C, based on a complete conformational analysis

The first quantum chemical calculation of the circular dichroism (CD) spectra of michellamines has been achieved, based on a complete quantum chemical conformational analysis. Michellamines are dimeric naphthylisoquinoline alkaloids and thus naturally occurring quateraryls, with a large molecular size and flexibility and equipped with stereogenic centers and axes.

Circular dichroism of naphthyldihydroisoquinoline alkaloids: Determination of the axial configuration of yaoundamine A

Abstract The absolute axial configuration of yaoundamine A, a naphthyldihydroisoquinoline alkaloid recently isolated from Ancistrocladus korupensis , was elucidated by comparison of experimental and theoretical Circular Dichroism (CD) spectra. An extensive semiempirical (AM1) analysis of the conformational properties of yaoundamine A and its atropodiastereomer revealed an interesting long-range mutual interaction of the local conformations in the axis and of the dihydroisoquinoline system via the 8-methoxy group as a “molecular clutch”. Subsequent calculation and Boltzmann-weighting of single-conformation CD spectra (CNDO/2S - C.I.) gave a thermal average CD spectrum matching the experimental one very closely.

Dioncophylline A, the Principal Cytotoxin from Ancistrocladus letestui

Abstract Using bioassay-guided fractionation, dioncophylline A [1] was isolated from the leaves and twigs of the tropical liana Ancistrocladus letestui Pelligr. Dioncophylline A was previously known from Triphyophyllum peltatum and A. abbreviatus. The in vitro cytotoxicity profile of 1 was characterized against the NCI panel of human tumor cell lines.