1,721,136 research outputs found
Fast atom bombardment mass spectrometry of carbobenzyloxy-protected amino acids and peptides
No full textThe positive fast atom bombardment (FAB) mass spectra of 15 N-carbobenzyloxy derivatives of α-amino acids are presented together with those of some synthetic peptides containing other widely employed protecting groups. The data obtained allow a fragmentation pattern to be established for the N-carbobenzyloxy moiety and to obtain detailed structural information on the main fragment ions. A study of the ion current ratio vs. time pattern shows that important fragments derive from the parent protonated molecule through FAB-induced condensed-phase reactions
Electron impact mass spectrometry of substituted 1,3,8-triazaspiro[4,5]decan-4-ones
No full textThe neuroleptic butyrophenone drug spiroperidol (8-[4-fluorophenyl)-4-oxobutyl]-1-phenyl-1,3,8-triazaspiro [4,5]decan-4-one) and related compounds are valuable tools for mapping the dopamine receptors in the brain. During the development of the radiochemical synthesis of these compounds with very short-lived isotopes suitable for positron emission tomography studies, positive electron impact mass spectrometric information was obtained. Ion series are present in the spectra of all 12 compounds studied, which unambiguously allow recognition of type and site of substitution on the spiro system
Convenient and expeditious synthesis of some indoloquinolizine alkaloids
No full textThe ambident reactivity of the imine-enamines (1) and (2) towards 1,3-dihalogenopropanes leads to an expeditious and efficient synthesis of some indoloquinolizines
Efficient synthesis of 1-ethyl-2,3,4,6,7,12-hexahydroindolo[2,3-α] quinolizine: A key precursor to eburnane alkaloids
No full textThe title compound has been conveniently synthesized from the imine (3) by cyclisation with acrylic acid followed by reduction
The configuration of (+)-evodiamine: A long-standing problem in the chemistry of indole alkaloids
No full textThe absolute configuration (S) of the long-known indole alkaloid (+)-evodiamine (1) has been established by correlation with (S)-tryptophan via (7S,13bS)-carboxyevodiamine (2)
A new tryptophan derived alkaloid from Evodia rutaecarpa (Juss.) Benth. et Hook
No full textThe first tryptophan-derived indolopyridoquinazoline alkaloid has been isolated from the fruits of Evodia rutaecarpa (Jussieu) Bentham et Hook. Its structure is deduced on the basis of spectral data and enantioselective synthesis. The compound has been assigned the absolute configuration (7 S,13b S)-7-carboxy-8,13,13b,14-tetrahydro-14-methylindolo[2′,3′:3,4]pyrido[2,1-b]quinazolin-5(7 H)-one
An efficient enantioselective approach to cyclic beta-amino acid derivatives via olefin metathesis reactions
No full textThe asymmetric synthesis of polyfunctionalized piperidine-and pyrrolidine-based scaffolds, specifically designed for the preparation of cyclic, conformationally constrained beta-amino acids, is realized combining a biocatalytic access to a versatile chiral building block with a wide range of transformations based on olefin metathesis
SYNTHETIC STUDIES ON INDOLE ALKALOIDS - A STEREOCONTROLLED ENTRY TO THE CUANZINE STRUCTURAL UNIT
No full textAn efficient synthesis of the cuanzine precursor 4d has been achieved beginning with 8-methoxy-dihydro-β-carboline 3b and utilizing as the key step the stereocontrolled alkylation of 16a (and/or 20a) followed by Hg(II)-induced heterocyclization. The structure and stereochemistry of 4d are thereby corroborated by chemical correlation with natural cuanzine 1a
Candida antarctica lipase B catalyzes the regioselective esterification of ecdysteroids at the C-2 OH
No full textImmobilized Candida antarctica lipase B (Novozym 435) catalyzes the regioselective acylation of 20R-hydroxyecdysone (1a) and its congeners 2a, 3a and 4a at the C-2 OH in high yield and purity. (C) 1997 Elsevier Science Ltd
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