Beta-hydrogen Atom Research Articles

Aromatization of 19-norandrogens by equine testicular microsomes.

In the stallion testis, aromatase activity was localized in the microsomal fraction. Androgen aromatization occurred through the loss of 1 beta,2 beta hydrogen atoms and appeared to involve free sulfhydryl groups. A single enzyme system seemed to aromatize androgen and norandrogen at the same rate while having a much lower affinity for norandrogens.

Mechanism of formation of the A/B cis ring junction of ecdysteroids in Polypodium vulgare.

1. The fates of the alpha-, 4 alpha- and 4 beta-hydrogen atoms of cholesterol during formation of the A/B cis ring junction of ecdysteroids was investigated by administration of [4-14C, 3 alpha-3H], [4-14C, 4 alpha-3H]- and [4-14C, 4 beta-3H]cholesterol species to the fern, Polypodium vulgare, and isolation of the 20-hydroxyecdysone formed in each case. 2. The 3H was retained in the ecdysteroid formed from each substrate. 3. Location of the 3H in the 20-hydroxyecdysone indicated that migration of 3H from the 3 alpha- and 4 beta-positions to C-4 and C-5, respectively, had occurred, whereas the 4 alpha-3H atom was retained at C-4. 4. A possible mechanism for the formation of the A/B cis ring junction of ecdysteroids in P. vulgare is presented.

Mechanistic and stereochemical studies on 3-oxo steroid delta 4-delta 5-isomerase from human placenta.

The mechanism of isomerization of delta 5-3-ox steroids to delta 4-3-oxo steroids was examined by using the membrane-bound 3-oxo steroid delta 4-delta 5-isomerase (EC 5.3.3.1) and the 3 beta-hydroxy steroid dehydrogenase present in the microsomal fraction obtained from full-term human placenta. (1) Methods for the preparation of androst-5-ene-3 beta, 17 beta-diol specifically labelled at the 4 alpha-, 4 beta- or 6-positions are described. (2) Incubations with androst-5-ene-3 beta, 17 beta-diol stereospecifically 3H-labelled either in the 4 alpha- or 4 beta-position showed that the isomerization reaction occurs via a stereospecific elimination of the 4 beta hydrogen atom. In addition, the complete retention of 3H in the delta 4-3-oxo steroids obtained from [4 alpha-3H]androst-5-ene-3 beta, 17 beta-diol indicates that the non-enzymic contribution to these experiments was negligible. (3) To study the stereochemistry of the insertion of the incoming proton at C-6, the [6-3H]androst-4-ene-3, 17-dione obtained from the oxidation isomerization of [6-3H]androst-5-ene-3 beta, 17 beta-diol was enzymically hydroxylated in the 6 beta-position by the fungus Rhizopls stolonifer. Retention of 3H in the 6 alpha-position of the isolated 6 beta-hydroxyandrost-4-ene-3, 17-dione indicates that in the isomerase-catalysed migration of the C(5) = C(6) double bond, the incoming proton from the acidic group on the enzyme must enter C-6 from the beta-face, forcing the existing 3H into the 6 alpha-position.

ChemInform Abstract: ABSOLUTE RATE CONSTANTS FOR REACTION OF THE TERT.‐BUTYLPEROXY RADICAL WITH 1‐BROMO‐2‐METHYLPROPANE AND 1‐CHLORO‐2‐METHYLPROPANE, KINETIC EVIDENCE FOR ANCHIMERIC ASSISTANCE IN THE ABSTRACTION OF A BETA‐HYDROGEN ATOM FOR ALKYL BROMIDES AND CHLORIDES

Chemischer InformationsdienstVolume 6, Issue 22 Preparative Organic Chemistry ChemInform Abstract: ABSOLUTE RATE CONSTANTS FOR REACTION OF THE TERT.-BUTYLPEROXY RADICAL WITH 1-BROMO-2-METHYLPROPANE AND 1-CHLORO-2-METHYLPROPANE, KINETIC EVIDENCE FOR ANCHIMERIC ASSISTANCE IN THE ABSTRACTION OF A BETA-HYDROGEN ATOM FOR ALKYL BROMIDES AND CHLORIDES J. H. BERNARD CHENIER, J. H. BERNARD CHENIERSearch for more papers by this authorJ. PAUL-ALAIN TREMBLAY, J. PAUL-ALAIN TREMBLAYSearch for more papers by this authorJAMES A. HOWARD, JAMES A. HOWARDSearch for more papers by this author J. H. BERNARD CHENIER, J. H. BERNARD CHENIERSearch for more papers by this authorJ. PAUL-ALAIN TREMBLAY, J. PAUL-ALAIN TREMBLAYSearch for more papers by this authorJAMES A. HOWARD, JAMES A. HOWARDSearch for more papers by this author First published: June 3, 1975 https://doi.org/10.1002/chin.197522205Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue22June 3, 1975 RelatedInformation

Alumina-catalyzed cleavage of ethers and thermal decomposition of aluminum alkoxides

A relation between the pyrolysis of aluminum alkoxides and the aluminacatalyzed decomposition of alcohols or ethers is shown by a comparison of products obtained from the reactions. Results of comparative studies with alcohols, ethers, and alkoxides that do not contain beta hydrogen atoms provide evidence for alcohol and ether decomposing over alumina via intermediate surface alkoxides. Kinetic results indicate that the decomposition of the intermediate alkoxide proceeds via a cyclic transition state.

A KINETIC ISOTOPE EFFECT STUDY OF THE TSCHUGAEFF REACTION

Three different kinetic isotope effects have been measured in the thermal decomposition of S-methyl-trans-2-methyl-1-indanyl xanthate: the S32/S34 effect for the thio-ether sulphur atom, the S32/S34 effect for the thion sulphur, and the C12/C13 effect for the carbonyl carbon. The results of these measurements provide strong support for a two-step mechanism, in which the rate-determining step is the removal through a cyclic transition state of the cis beta hydrogen atom by the thion sulphur atom.