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.

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.

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.

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.