125 research outputs found
Mass spectrometry of heterocyclic compounds VIIIâelectronâimpactâinduced fragmentation of 1,2âdiphenylâpyrazolidineâ3,5âdione and some 4âsubstituted derivatives
No full textThe mass spectra of 1,2-diphenylâpyrazolidine-3,5-dione and twentyâone 4âsubstituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4âposition of the heterocycle and/or from the Ãâposition of the 4âsubstituent groups, lead to the main primary fragment ions [C12H11N2]+ (m/e 183) as shown by the metastables. The 4,4âd2 derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4âunsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4âderivatives by the loss of 4âsubstituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C3O2 and C3HO2. Important rearrangements leading to elimination of C6H6N and C6H7N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electronâimpact and/or thermal decompostion of some complex compounds containing more than one 1,2âdiphenylâpyrazolidineâ3,5âdione system. The [C6H5N2]+ (m/e 105) and [C6H5]+ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4âsubstituent groups can be excluded. Copyright © 1975 Heyden & Son Ltd
Enantioselective total synthesis and absolute configuration of the alleged structure of crassinervic acid
No full textAn enantioselective synthesis of the structure reported for the natural antifungal compound, (-)-crassinervic acid (1), has been achieved starting from geraniol and p-hydroxybenzoic acid. The key chirality-inducing step is a Sharpless asymmetric epoxidation of an allylic alcohol, on the basis of which the S configuration can be assigned to the (-) natural enantiomer. The discrepancies between the spectroscopic data for synthetic and natural crassinervic acid cast some doubts on the structure assigned to the natural compound. A possible revised structure is discussed
Total synthesis of the natural product benzo[j]-fluoranthene-4, 9-diol : an approach to the synthesis of oxygenated benzo[j]fluoranthenes
No full textA synthetic sequence to the benzo[j]fluoranthene nucleus is described. Crucial steps of the procedure include a Suzuki coupling between appropriately substituted 2-bromo-acenaphthylene-1-carbaldehydes and 2-formylbenzeneboronates followed by McMurry ring closure. The synthesis represents a new approach to the benzo[j]fluoranthene ring system and specifically provides a method for the rapid preparation of differently substituted derivatives. Following this strategy, the first total synthesis of the recently isolated natural product benzo[j]fluoranthene-4,9-diol was carried out
Synthesis, Modeling, and RET Protein Kinase Inhibitory Activity of 3-and 4-Substituted beta-Carbolin-1-ones
No full textA series of beta-carbolin-2-ones and 3,10-dihydro-2H-azepino[3,4-b]indol-1-ones have been designed, synthesized, and evaluated as RET protein kinase inhibitors on the basis of their structural similarity with the prototype indolin-2-one RPI-1. Some beta-carbolin-2-ones (structure 2) showed an ability to inhibit RET enzymatic activity in vitro and proliferation of RETC634R oncogene-transformed NIH3T3 cells comparable to that of the reference compound. The docking analysis of the interaction of these compounds with the crystallographic structure of RET tyrosine kinase domain suggested a new binding interaction scheme different from the one proposed during their design. The rigid structure of the compounds of this series represents a new scaffold with potential advantages in the design of RET protein kinase inhibitors
Total Synthesis of Berkeleyamide A and its 10-epi Isomer
No full textA short and efficient synthesis of the novel cytotoxic natural product berkeleyamide A, isolated from a deep-water Penicillium rubrum, has been accomplished. L-Leucinol was used as the only chiral starting material. A diastereoselective aldol condensation is the key step in the synthesis
Enantiodifferentiation in taste perception of isovanillic derivatives
No full textBoth enantiomers of isovanillic chiral 1,3-oxathianes, e.g. I, II, and III, and a 1,3-dithiane IV were obtained as pure compds. by asym. synthesis or chiral HPLC resoln. Their abs. configurations were established using x-ray crystal structure anal., CD spectroscopy, or NMR NOE expts. The relationships between the structure and the sweet taste of the enantiomeric compds. were discussed
Synthesis, Modeling, and RET Protein Kinase Inhibitory Activity of 3- and 4-substituted Beta-carbolin-1-ones
No full textA series of beta-carbolin-2-ones and 3,10-dihydro-2H-azepino[3,4-b]indol-1-ones have been designed, synthesized, and evaluated as RET protein kinase inhibitors on the basis of their structural similarity with the prototype indolin-2-one RPI-1. Some beta-carbolin-2-ones (structure 2) showed an ability to inhibit RET enzymatic activity in vitro and proliferation of RETC634R oncogene-transformed NIH3T3 cells comparable to that of the reference compound. The docking analysis of the interaction of these compounds with the crystallographic structure of RET tyrosine kinase domain suggested a new binding interaction scheme different from the one proposed during their design. The rigid structure of the compounds of this series represents a new scaffold with potential advantages in the design of RET protein kinase inhibitors
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