High resolution x-ray analysis of two mutants of a curaremimetic snake toxin.

A previous mutational analysis of erabutoxin a (Ea), a curaremimetic toxin from sea snake venom, showed that the substitutions S8G and S8T caused, respectively, 176-fold and 780-fold affinity decreases for the nicotinic acetylcholine receptor (AchR). In view of the fact that the side-chain of Ser8 is buried in the wild-type toxin, we wondered whether these affinity changes reflect a direct binding contribution of S8 to the receptor and/or conformational changes that could have occurred in Ea as a result of the introduced mutations. To approach this question, we solved X-ray structures of the two mutants S8G and S8T at high resolution (0.18 nm and 0.17 nm, with R factors of 18.0% and 17.9%, respectively). The data show that none of the mutations significantly modified the toxin structure. Even within the site where the toxin binds to the receptor the backbone conformation remained unchanged. Therefore, the low affinities of the mutants S8T and S8G cannot be explained by a large conformational change of the toxin structure. Although we cannot exclude the possibility that undetectable structural changes have occurred in the toxin mutants, our data support the view that, although buried between loop I and II, S8 is part of the functional epitope of the toxin.

Alkaloids from Psychotria oleoides with activity on growth hormone release.

Bioactivity-guided purification of a crude alkaloid extract of Psychotria oleoides has afforded a new alkaloid, psycholeine [1], together with quadrigemine C [2], a tetrameric pyrrolidinoindoline compound of unknown stereochemistry. A comparison study of nmr and cd spectra of quadrigemine C and hodgkinsine [3], a trimeric pyrrolidinoindoline substance, led us to suggest the stereochemistry of quadrigemine C. The structure and configuration of psycholeine was determined by spectroscopic means and chemical correlation with quadrigemine C. Psycholeine interacts with somatostatin receptors and exhibits a somatostatin antagonistic activity on GH secretion by pituitary cells in primary culture.

Isolation and 2D NMR Studies of Alkaloids from Comptonella sessilifoliola1.

Six known furanoquinoline alkaloids have been isolated from the wood and trunk bark of COMPTONELLA SESSILIFOLIOLA (Guillaumin) Hartley (Rutaceae). 2D NMR experiments gave the assignment of all the signals for both (1)H- and (13)C-NMR spectra. Pteleine and kokusaginine were used as models. The two-dimensional carbon-proton correlation experiments, performed for the first time on furanoquinoline alkaloids, led us to correct (13)C-NMR assignments previously described in the literature.

Iridoids and an Alkaloid from Oxera morieri1.

A novel monoterpene alkaloid, oxerine, has been isolated from the aerial parts of OXERA MORIERI. Its structure 7 has been elucidated on the basis of its spectral data and its sterochemistry established by its synthesis, using harpagide as starting material. Five iridoids and verbascoside have also been isolated from the plant material.

Iridoids from Scaevola racemigera1.

Five iridoids have been isolated from the aerial parts of SCAEVOLA RACEMIGERA Däniker, namely, loganin, loganic acid, sylvestroside III, cantleyoside, and scaevoloside. This latter is a novel compound whose structure 1 has been elucidated on the basis of its spectral data, mainly (1)H- and (13)C-NMR.

[Plants from New Caledonia. Alkaloids from Sarcomelicope dogniensis Hartley stem bark]. / Plantes de Nouvelle-Calédonie. Alcaloïdes des écorces de Sarcomelicope dogniensis Hartley.

Two new pyranofuroquinoline alkaloids, cis-1,2-dihydroxy-1,2 dihydroacronydine 2 and trans-1,2-dihydroxy-1,2-dihydroacronydine 3 have been isolated from Sarcomelicope dogniensis stem bark. Their structures have been elucidated by spectral analysis and chemical correlations. In addition, 11 other alkaloids have been isolated from the stem bark of this species.

[Plants in New Caledonia. Iridoids from Scaevola montana Labill]. / Plantes de Nouvelle-Calédonie. Iridoïdes de Scaevola montana Labill.

Five iridoids have been isolated from the aerial parts of Scaevola montana Labill., namely loganin, sylvestroside III, sylvestroside III dimethylacetal, cantleyoside and cantleyoside dimethylacetal. Their structures have been elucidated on the basis of their spectral data, mainly chemical ionisation mass spectrometry and 1H-NMR spectroscopy.

Biogenesis of proteaceous alkaloids.

A scheme is presented which outlines the possible mode of biogenesis of alkaloids so far reported from the proteaceous plants Bellendena montana and Agastachys odorata (both from Tasmania), Darlingia darlingiana and D. ferruginea (from Queensland) and Knightia deplanchei and K. strobilina (from New Caledonia).