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Ch. Meystre

Bio: Ch. Meystre is an academic researcher from Ciba Specialty Chemicals. The author has contributed to research in topics: Aldosterone & Silver acetate. The author has an hindex of 20, co-authored 40 publications receiving 915 citations.

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Journal ArticleDOI
TL;DR: In this article, the reactions of 20-hydroxypregnanes with iodine and lead tetraacetate, mercuric or silver acetate yield the corresponding oxy radicals, and with the latter two reagents, 20-hypoiodites are definitely intermediates.
Abstract: The reactions of 20-hydroxypregnanes with iodine and lead tetraacetate, mercuric or silver acetate yield the corresponding oxy radicals. With the latter two reagents, 20-hypoiodites are definitely intermediates. The primary reaction products, i.e. 18-iodo-20-hydroxy compounds, can be oxidized and hydrolized to 18-hydroxy-20-oxo-pregnanes. Under suitable conditions, especially with lead tetraacetate and iodine, a second substitution reaction on carbon 18 of the 18-iodo-20-hydroxy-pregnanes takes place, leading to compounds of the (18 20)-hemiacetal type. These can be oxidized to (18 20)-lactones.

83 citations

Journal ArticleDOI
TL;DR: In this article, a method was described which enables the production in only one chemical step of 1,4-bisdehydro-3-oxo-steroids inter alia from 3-oxO- steroids saturated in ring A or from α β-mono-unsaturated 3-ketones.
Abstract: A method is described which enables the production in only one chemical step of 1,4-bisdehydro-3-oxo-steroids inter alia from 3-oxo- steroids saturated in ring A or from the α β-mono-unsaturated 3-ketones. The dehydrogenating agent is selenium dioxide and the solvent a tertiary alcohol preferably containing some acid.

71 citations

Journal ArticleDOI
TL;DR: It is shown that 20-hydroxy-18-C-radicals combine with iodine atoms, to give 18-iodides which can befurther substituted through radicals to give potential 18-oxo-compounds in high yield.
Abstract: The intramolecular substitution of the angular methyl groups in steroids by attack of O-radicals derived from 6β-, 11β, and 20-alcohols is discussed. Irrespective of their genesis, these radicals abstract a hydrogen atom from one of the said methyl groups, suitably oriented inδ-position. The C-radicals thus formed give different products depending on the neighbouring groups. It is shown that 20-hydroxy-18-C-radicals combine with iodine atoms, to give 18-iodides which can befurther substituted through radicals to give potential 18-oxo-compounds in high yield. In the case of 20-cyanohydrines, the intramolecular reaction of the 18-C-radical with the cyano groups gives rise to the new 18-cyano-20-oxo-steroids. With 6β- and 11β-O-radicalssingle substitution in 19-position predominates, since the steric arrangement of the primary product favours the intramolecular ether formation over a second substitution reaction. A general reaction scheme for these transformations is proposed.

63 citations

Journal ArticleDOI
TL;DR: A simple and efficient method for the production of various 19-nor-androstenes from dehydroepiandrosterone is described.
Abstract: A simple and efficient method for the production of various 19-nor-androstenes from dehydroepiandrosterone is described.

48 citations


Cited by
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Journal ArticleDOI
TL;DR: A review of the metabolism of AAS is presented and Testosterone is the principal androgenic steroid and its metabolism is compared with that of Aas.
Abstract: Anabolic androgenic steroids (AAS) are misused to a high extent in sports by athletes to improve their physical performance. Sports federations consider the use of these drugs in sports as doping. The misuse of AAS is controlled by detection of the parent AAS (when excreted into urine) and (or) their metabolites in urine of athletes. I present a review of the metabolism of AAS. Testosterone is the principal androgenic steroid and its metabolism is compared with that of AAS. The review is divided into two parts: the general metabolism of AAS, which is separated into phase I and phase II metabolism and includes a systematic discussion of metabolic changes in the steroid molecule according to the regions (A-D rings), and the specific metabolism of AAS, which presents the metabolism of 26 AAS in humans.

344 citations

Journal ArticleDOI
TL;DR: Exretion studies with the most common anabolic steroids were performed and the main excreted metabolites were synthesized for bolasterone, boldenone, 4-chlorodehydromethyltestosterone, clostebol, drostanolone, fluoxymesterone, formebol one, mestanolone, mesterolone and metandienone.

275 citations

Journal ArticleDOI
TL;DR: The history, recent advances, and mechanistic underpinnings of intramolecular HAT are outlined as a guide to addressing ongoing challenges in this arena.
Abstract: The selective functionalization of remote C–H bonds via intramolecular hydrogen atom transfer (HAT) is transformative for organic synthesis This radical-mediated strategy provides access to novel reactivity that is complementary to closed-shell pathways As modern methods for mild generation of radicals are continually developed, inherent selectivity paradigms of HAT mechanisms offer unparalleled opportunities for developing new strategies for C–H functionalization This review outlines the history, recent advances, and mechanistic underpinnings of intramolecular HAT as a guide to addressing ongoing challenges in this arena 1 Introduction 2 Nitrogen-Centered Radicals 21 sp 3 N-Radical Initiation 22 sp 2 N-Radical Initiation 3 Oxygen-Centered Radicals 31 Carbonyl Diradical Initiation 32 Alkoxy Radical Initiation 33 Non-alkoxy Radical Initiation 4 Carbon-Centered Radicals 41 sp 2 C-Radical Initiation 42 sp 3 C-Radical Initiation 5 Conclusion

268 citations

Journal ArticleDOI
TL;DR: The present progress report surveys recent developments in the formation of O-glycosidic bonds starting from 1-halo sugars and from sugar 1,2-orthoesters.
Abstract: Considerable problems attend the synthesis of biologically important natural products whose carbohydrate components display a greater or lesser degree of complexity. The present progress report surveys recent developments in the formation of O-glycosidic bonds starting from 1-halo sugars and from sugar 1,2-orthoesters. Particular emphasis is placed on attempts to reach a better understanding of the steric course of glycosylation reactions on the basis of mechanistic considerations. Studies on the silver-salt dependence of the Koenigs-Knorr synthesis led to improvements in preparative applications and to new concepts concerning the reaction course. The introduction of sugar 1,2-orthoesters as glycosylation components has greatly enriched our preparative armoury for the synthesis of trans glycosides. Remarkable progress has also been made in the synthesis of cis glycosides, in part by exploiting novel neighbouring group effects.

260 citations

Journal ArticleDOI
TL;DR: The purification of a tyrosinase from cell-free extracts of Streptomyces glaucescens is described, and the enzyme obtained is homogeneous according to the criteria of ultracentrifuge analysis and polyacrylamide gel electrophoresis, which shows optimal activity at pH 6.8.
Abstract: 1 The purification of a tyrosinase from cell-free extracts of Streptomyces glaucescens is described. The enzyme obtained is homogeneous according to the criteria of ultracentrifuge analysis and polyacrylamide gel electrophoresis. 2 An average molecular weight of 29100 was determined by dodecylsulfate-gel electrophoresis and by sedimentation equilibrium analysis in the ultracentrifuge. The amino acid composition of the pure enzyme is also reported. 3 The enzyme contains one atom of copper in the cuprous form per molecule and is strongly inhibited by KCN and 4-nitro-catechol. 4 The enzyme shows optimal activity at pH 6.8; it has an isoelectric point at pH 6.95 and is most stable at pH 8.0. 5 Variations of Km values between pH 5.0 and 8.9 when l-tyrosine methylester and 3,4-di-hydroxy-l-phenylalanine were used as substrate was interpreted by assuming that different ionizable groups are involved in the oxidation of these two substrates. 6 The Michaelis-Menten constants and KCat are strongly dependent on the oxygen concentration for 3,4-dihydroxy-l-phenylalanine and almost independent for l-tyrosine methyl ester. Kinetic parameters obtained for a series of mono- and o-diphenol substrates are also reported.

189 citations