The Experts below are selected from a list of 42 Experts worldwide ranked by ideXlab platform
R Samy - One of the best experts on this subject based on the ideXlab platform.
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chemistry of Cyclic Tautomers of tryptophan formation of a quaternary center at c3a and total synthesis of the marine alkaloid ent debromoflustramine b
Journal of Organic Chemistry, 1994Co-Authors: Milan Bruncko, David Crich, R SamyAbstract:A diastereoselective synthesis of the unnatural (+)-enantiomer of the marine alkaloid (-)-debromoflustramine B (1) from a Cyclic Tautomer (9) of L-tryptophan is described. The optical rotation of the synthetic 1 is opposite to that of the natural material enabling the configuration of the natural product to be established as 3aS,8R. As natural flustramine B has been converted to (-)-debromoflustramine B its absolute configuration may also be set as 3aS,8aR. The synthetic scheme involves radical bromination of 9 at C3a followed by allylation, at C3a, with allyltributyltin to give 21. The allyl group is then converted to the C3a prenyl derivative 23 by oxidative cleavage and Wittig reaction. The remainder of the synthesis involves removal of the now extraneous carbomethoxy group from C2 and selective removal of the two nitrogen protecting groups and alkylation of the resulting amines. Oxidation of 9 with ceric ammonium nitrate to give mixtures of the C3a nitrato- and hydroxy-derivatives 18 and 19 is also described
Milan Bruncko - One of the best experts on this subject based on the ideXlab platform.
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chemistry of Cyclic Tautomers of tryptophan formation of a quaternary center at c3a and total synthesis of the marine alkaloid ent debromoflustramine b
Journal of Organic Chemistry, 1994Co-Authors: Milan Bruncko, David Crich, R SamyAbstract:A diastereoselective synthesis of the unnatural (+)-enantiomer of the marine alkaloid (-)-debromoflustramine B (1) from a Cyclic Tautomer (9) of L-tryptophan is described. The optical rotation of the synthetic 1 is opposite to that of the natural material enabling the configuration of the natural product to be established as 3aS,8R. As natural flustramine B has been converted to (-)-debromoflustramine B its absolute configuration may also be set as 3aS,8aR. The synthetic scheme involves radical bromination of 9 at C3a followed by allylation, at C3a, with allyltributyltin to give 21. The allyl group is then converted to the C3a prenyl derivative 23 by oxidative cleavage and Wittig reaction. The remainder of the synthesis involves removal of the now extraneous carbomethoxy group from C2 and selective removal of the two nitrogen protecting groups and alkylation of the resulting amines. Oxidation of 9 with ceric ammonium nitrate to give mixtures of the C3a nitrato- and hydroxy-derivatives 18 and 19 is also described
David Crich - One of the best experts on this subject based on the ideXlab platform.
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chemistry of Cyclic Tautomers of tryptophan formation of a quaternary center at c3a and total synthesis of the marine alkaloid ent debromoflustramine b
Journal of Organic Chemistry, 1994Co-Authors: Milan Bruncko, David Crich, R SamyAbstract:A diastereoselective synthesis of the unnatural (+)-enantiomer of the marine alkaloid (-)-debromoflustramine B (1) from a Cyclic Tautomer (9) of L-tryptophan is described. The optical rotation of the synthetic 1 is opposite to that of the natural material enabling the configuration of the natural product to be established as 3aS,8R. As natural flustramine B has been converted to (-)-debromoflustramine B its absolute configuration may also be set as 3aS,8aR. The synthetic scheme involves radical bromination of 9 at C3a followed by allylation, at C3a, with allyltributyltin to give 21. The allyl group is then converted to the C3a prenyl derivative 23 by oxidative cleavage and Wittig reaction. The remainder of the synthesis involves removal of the now extraneous carbomethoxy group from C2 and selective removal of the two nitrogen protecting groups and alkylation of the resulting amines. Oxidation of 9 with ceric ammonium nitrate to give mixtures of the C3a nitrato- and hydroxy-derivatives 18 and 19 is also described
Tohru Hino - One of the best experts on this subject based on the ideXlab platform.
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Chemistry of the Cyclic Tautomer of tryptophans
YAKUGAKU ZASSHI, 1996Co-Authors: Tohru HinoAbstract:A historical development of the chemistry of Cyclic Tautomer of tryptophan is reviewed. The Cyclic Tautomer of tryptophan, pyrrolo [2,3-b]indole-2-carboxylic acid, was prepared by dissolving N-methoxycarbonyltryptophan ester derivatives in 85% phosphoric acid or trifluoroacetic acid. The Cyclic Tautomer can be reverted to the indolic form with a dilute acid. The Cyclic Tautomer is an aniline derivative and the enamine reactivity of the indole ring in tryptophan is protected. The electrophilic substitution and oxidation of these Cyclic Tautomers opened a new method to prepare 5-substituted and/or 6-substituted tryptophan derivatives such as 5-bromo-, 5-hydroxy, and 6-methoxy-tryptophans. The formation and reactions of Cyclic Tautomers of diketopiperazines containing tryptophan and 3-indoleacetamide are also discussed. Some indole alkaloids having substituents at the benzene ring such as fumitremorgins, flustramine B, and eudistomines were synthesized by the use of these reactions. Furthermore, enantioselective alkylations of the carbanion at the 2-position of the Cyclic Tautomer established a new route to optically pure alpha-substituted tryptophans. The 2,3-dehydro derivative of the Cyclic Tautomer is an alpha, beta-unsaturated ester and was found to be a good precursor of optically pure beta-substituted tryptophans. The 3a-position of the Cyclic Tautomer is a benzylic position and subjected to radical reactions to give 3a-substituted-pyrroloindoles.
Aleksey V. Varlamov - One of the best experts on this subject based on the ideXlab platform.
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Ring-chain Tautomerism in the products of the reaction between 5-substituted furfurylamines and anhydrides of α,β-unsaturated carboxylic acids
Chemistry of Heterocyclic Compounds, 2016Co-Authors: Fedor I. Zubkov, Victor D. Golubev, Vladimir P. Zaytsev, Olga V. Bakhanovich, Evgeniya V. Nikitina, Victor N. Khrustalev, Rinat R. Aysin, Tatiana V. Timofeeva, Roman A. Novikov, Aleksey V. VarlamovAbstract:The reactions of 5-substituted furfurylamines with anhydrides of α,β-unsaturated carboxylic acids (acryloyl chloride and maleic anhydride) were studied. The first step of the reaction mechanism involved acylation of furfurylamine nitrogen atom, followed by a stereospecific, spontaneous intramolecular Diels–Alder reaction at the furan ring of the N -furfurylamide intermediates. When the starting materials were 5-alkyl-substituted furfurylamines, the expected 1-oxo-2,3,7,7a - hexahydro-1 H -3a,6-epoxyisoindoles or the corresponding 7-carboxylic acids were obtained in up to 98% yields. The acylation of 5-aryl-substituted furfurylamines with maleic anhydride led to N -furfurylmaleic amides, which formed a dynamic equilibrium in solutions with adducts formed by intramolecular [4+2] cycloaddition, 3a,6-epoxyisoindole-7-carboxylic acids, as proved by NMR spectroscopy. X-ray structural analysis results show that these mixtures crystallized in the form of the Cyclic Tautomer.
