bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of dl‐erythro and threo‐sphingosine‐4,5‐3H
Authors: Gal Andrew E. 
Published: October 2006

AbstractDL‐erythro‐sphingosine and DL‐threo‐sphingosine specifically labelled with 3H in positions 4 and 5 were prepared. The synthesis of these compounds was based on a modification of a procedure published by Grob and Gadient. Quantitative separation of the sphingosines from acetylenic impurities was accomplished, and the physical constants of pure DL‐erythro and threo sphingosines were determined. D‐erythro sphingosine was prepared by resolving the DL racemate and it was found identical to the naturally occurring product.
Synthesis of tritium labelled diphenhydramine hydrochloride (benadryl )
Authors: Blackburn C. E. , Ober R. E. 
Published: October 2006

AbstractThe synthesis and characterization of tritium‐labelled diphenhydramine hydrochloride is described. An attempt to label diphenhydramine directly with tritium by an exchange reaction (CH3COOH, 10 c 3H2O, Pt) resulted in a mixture of tritiated benzophenone, benzhydrol, diphenhydramine, and other products. A mixture of tritiated benzophenone and benzhydrol was isolated, reduced to benzhydrol‐3H, and then condensed with dimethylaminoethanol to yield diphenhydramine‐3H with the label in the benzhydryl group.
Synthese von Testosteron‐17α‐T und Hydrocortison‐11α‐T
Authors: Christ W. , Wenzel M. , Schulze P. E. 
Published: October 2006

AbstractFor the in vivo‐measurements of the oxidation of steroid‐alcohols to steroid‐ketones testosterone‐17α‐T and hydrocortisone‐11α‐T were synthesized by the reduction of the corresponding 17‐ or 11‐ketones with LiBT4 after ketalization of the other keto‐groups with aethylenglycol. Purification from radioactive by‐products in analytical and preparative scale was easely achieved by thin‐layer‐chromatography combined with automatic scanning of the radioactivity by the 2‐dimensional Berthold‐«Dünnschicht‐Scanner».
The synthesis of L‐14C‐serine ethanolamine phosphate, L‐Serine 1,2‐14C‐ethanolamine phosphate, L‐3H‐Serine 1,2‐14C‐ethanolamine phosphate, and related compounds
Authors: Porcellati G. 
Published: October 2006

AbstractA procedure for the chemical synthesis of the following labelled phosphodiesters : L‐14C‐serine ethanolamine phosphate, L‐serine 14C‐ethanolamine phosphate, L‐3H‐serine 14C‐ethanolamine phosphate, L‐14C‐threonine ethanolamine phosphate, L‐threonine 14C‐ethanolamine phosphate, L‐14C‐serine L‐14C‐serine phosphate and L‐14C‐threonine L‐14C‐threonine phosphate is reported. The variously labelled forms of these phosphodiesters have been synthesized and purified by a route and a procedure leading to unequivocal structures for the products. The labelled L‐serine L‐serine phosphate and L‐threonine L‐threonine phosphate have been obtained as by‐products in the preparation of the labelled forms of L‐serine ethanolamine phosphate and L‐threonine ethanolamine phosphate, respectively.
Preparation of labelled lipids
Authors: Mangold Helmut K. 
Published: October 2006

AbstractIn the present review emphasis is placed on the description of advances made in the synthesis and biosynthesis of labelled neutral lipids as well as phosphatides and other complex ionic lipids. Methods applicable to the analysis and purification of these compounds are described briefly. In addition observations related to the autoradiolysis of labelled lipids during storage are discussed.
Die Herstellung von 14C markiertem β‐Chloräthyl‐trimethylammonium‐chlorid (CCC)
Authors: Chwala Ch. 
Published: October 2006

AbstractEs wird die Herstellung von β‐Chloräthyl‐trimethylammoniumchlorid (Methyl‐14C) = CCC‐(Methyl‐14C) und CCC‐1,2‐14C beschrieben. Das Verfahren zur Markierung der CH3‐Gruppe ist gegenüber bereits bekannten durch seine Einfachheit ausgezeichnet. Für die Markierung der beiden CH2‐Gruppen des CCC gingen wir von Athylenoxyd‐1,2‐14C aus. Die Ausbeuten betrugen in beiden Fällen, auch betreffend die eingesetzte Aktivität, über 90 %. Die Aktivitätsmessung wurde nach katalytischer Verbrennung zu CO2 in Gaszählrohren im Proportionalbereich ausgeführt. Es wird die Reinigung und Prüfung der radiochemischen Reinheit der erhaltenen Substanzen beschrieben.
Isotopic labelling studies in irradiated organic solutions
Authors: Burr J. G. , Cher M. , Yang J. Y. 
Published: October 2006

AbstractNon‐linear interactions between solvent and solute are observed in the radiolysis of binary organic mixtures. The use of labelled molecules to diagnose both the nature of the excited solvent species and also the nature of the interaction between these excited secties and the solute molecules will be described.The particular systems discussed in detail will be: 1. cyclohexane + 14C‐benzene; 2. tritiated cyclohexane + 14C‐benzene; 3. tritiated cyclohexane + benzoquinone; 4. tritiated cyclohexane + cyclopentene; 5. cyclohexane + 14C‐cyclohexene; 6. cyclohexane or cyclohexane d12 + benzene or benzene‐d6; 7. cyclohexane‐d12 + cyclopentane; 8. various mixture of cyclohexane, cyclopentane and deuterated analogs with corresponding olefins and the deuterated olefins; 9. mixtures of light and heavy water vapor with cyclopentane, methane, cyclohexane and other hydrocarbons.Analysis of the products obtained in the irradiation of these systems has been informative about the nature of the quenching and scavenging processes wich take place and also about the nature of the, reactive species involved.
The simple preparation of mevalonic‐3′, 4‐D Acid and ‐3′, 4‐T Acid
Authors: Matsuo Mitsuyoshi , Kasida Yosihiko 
Published: October 2006

AbstractMevalonic‐3′, 4‐D acid and –3′, 4‐T acid were synthesized by using deuterated and tritiated Ivater and the total yield of the labelled MV A was 6.5 %. The specific activity of the tritiated MV A, which was derived from 2.3 g. of tritiated water (250 mCi), was 1.77 mCi./mM.
The production of 15N‐labelled S‐adenosylmethionine and adenine by yeast biosynthesis
Authors: Zappia V. , Salvatore F. , Zydek C. R. , Schlenk F. 
Published: October 2006

AbstractA method for the biosynthesis of 15 N‐labelled S‐adenosylmethionine from 15 NH4+ and L‐methionine by yeast is reported. Culture conditions suitable for economy in the utilization of the isotope were developed, and the use of γ‐irradiated yeast (1 Mrad) for this purpose was explored. The irradiated yeast proved as effective as non‐irradiated yeast, but it did not offer any advantage. 15 N‐Adenine was obtained from S‐adenosylmethionine by hydrolysis; its isolation by ion exchange chromatography is described.
Préparation de l'acide succinique (14C‐1) par oxydation de l'acide allylacétique (Carboxyle 14C)
Authors: Herbert M. , Pichat L. , Fabignon Mlle C. 
Published: October 2006

Allylacetic acid 1‐14C prepared by carbonation of 3‐butenyl‐magnesium bromide is oxidized into succinic acid 1‐14C by periodic acid and a catalytic amount of K MnO4. After purification by chromatography on a column of Dowex 1 × 10 Cl−, succinic acid 1‐14C is secured with an over all yield of 66 % based on Ba 14CO3 specific activity 37.4 mCi /mM. This method is more convenient than those of the literature because it avoids the preparation of K 14CN and affords a better yield.L'acide allylacétique (carboxyl14C) obtenu par carbonatation du bromure de butène‐3 ylmagnésium est oxydé en acide succinique (14C‐1) par l'acide periodique en présence de quantités catalytiques de permanganate de potassium. Après purification par chromatographie sur résine échangeuse Dowex 1 × 10 Cl−, l'acide succinique (14C‐1) est obtenu avec un rendement global de 66 % calculé sur 14CO3Ba; activité spécifique 37,4 mCi/mM. Les avantages de cette méthode sur celles de la littérature sont d'éviter la préparaation du cyanure de potassium (14C) et un meilleur rendement global.
Synthèse de la DL‐ Arginine (14C ‐ 1)
Authors: Pichat L. , Guermont J. P. , Liem Phung Nhu 
Published: October 2006

DL Arginine (14C‐1) is prepared by a Strecker reaction with γ‐guanidobutyraldehyde and K14CN. Radioactive and chemical yields are 60 % based on K14CN.La DL‐Arginine (14C‐1) a été obtenue par réaction de Strecker à partir de l'aldéhyde γ‐guanido butyrique et du cyanure de potassium (14C) avec des rendements chimiques et radioactifs de l'ordre de 60 % par rapport à K14CN.
14C‐labelled 4‐hydroxycoumarin derivatives. II. Synthesis of 3‐n‐hexyl‐4‐hydroxycoumarin‐10‐14C
Authors: Susan A. B. , Avramescu A. , Dinescu M. 
Published: October 2006

AbstractThe synthesis and characterization of 3‐n‐hexyl‐4‐hydroxycoumarin‐10‐14C is described. This new labelled substance was prepared by starting from phenol‐1‐14C which was transformed in a single step into the final product by a ZnCl2 and POCl3 catalysed condensation with n‐hexyl‐malonic acid.
Preparation of tritium labelled L‐phenylalanine
Authors: Gerday Ch. , Verly W. G. 
Published: October 2006

AbstractTritiated N‐chloracetyl‐DL‐phenylalanine, obtained by reduction of the N‐chloracetyl‐dehydrophenylalanine with tritiated hydrogen, is hydrolysed by carboxypeptidase A. The method gives L‐phenyl‐alanine‐2,3‐3H of high optical purity and with any specific activity up to 60 curies per millimole.
The preparation and stability of DL‐α‐tocopherol labelled with tritium at high specific activity
Authors: Evans E. A. , Phillips R. F. 
Published: October 2006

AbstractHydrogen‐tritium exchange labelling methods proved to be unsatisfactory for the preparation of tritiated DL‐α‐tocopherol at high specific activity. The preparation of α‐tocopherol specifically labelled in the 5‐methyl hydrogen positions is described : the method permits specific activities in the curies per millimole range to be readily achieved. The synthesis is also suitable for preparing tocopherol doubly labelled with tritium and carbon‐14. The stability of the tritiated vitamin on storage is discussed.
Labelling of synthetic oestrogens of the trans‐stilbene and symmetrical diphenylethane series by catalytic exchange on heterogenous platinum
Authors: Claringbold P. J. , Garnett J. L. , O'Keefe J. H. 
Published: October 2006

AbstractSynthetic oestrogens of the trans‐stilbene and sym. diphenyl‐ethane series have been labelled by catalytic exchange with isotopic water in the presence of heterogeneous platinum. Experiment showed that platinum oxide pre‐reduced with sodium borohydride produced a more suitable catalyst for the exchange than the alternative of self‐activation. Self‐activated catalysts accentuated degradation of the substrate. The labelling method was suitable for the tritiation of all ten substances studied and also for their deuteration with the exception of 4,4′‐dimethoxy‐α‐chloro‐α‐methyl stilbene. Methoxy groups on the aromatic rings sterically hinder exchange in adjacent positions. Steric hindrance to labelling of hydrogens on the bridge carbon atoms was also noted. The results are shown to be consistent with a π‐complex adsorption mechanism.
Enzymatic degradation of sugars
Authors: Sturani E. , Cocucci S. 
Published: October 2006

AbstractA quick and convenient procedure for the degradation of sugars has been worked out. The quantitative conversion of glucose to lactic acid by the use of commercially available enzymes, followed by the chemical degradation of the latter compound, allows to discriminate between the carbons 1 and 6, 2 and 5, 3 and 4 of the molecule. Moreover the enzymatic conversion of glucose to glycerol‐1‐phosphate and to 3‐phosphoglyceric acid allows to separate the glucose molecule into the two moieties, that is to discriminate between carbons 1, 2, 3 and 4, 5, 6.The problems and the results of this degradation procedure are discussed.
Specific 3H‐labelling by diimide reduction of unsaturated bonds. II. Methods and applications of labelling
Authors: Koch G. K. 
Published: October 2006

AbstractMethods for specific labelling of alkyl groups on a mCi/mmole level are described, in which double bonds are hydrogenated with labelled diimide and in which tritiated water is used as the source of the label. In one method, labelled diimide is obtained by exchange labelling and oxidation of hydrazine in acetonitrile and in the other, potassium azodicarboxylate is decomposed with labelled hydrogen ions in a pyridine medium. Molar specific activities of 8 and 20 % of the original water are obtained. The latter method is preferred for reproducible quantitative conversions of unsaturated fatty acids and methyl esters on a 10–100 mg scale.By partial oxidation with permanganate in acetone, both the specificity of diimide labelling and the usefulness of permanganate degradation for the localization of tritium labels in fatty acids were demonstrated. The possible application of a combination of diimide labelling and oxidative degradation for the determination of the structure of polyunsaturated acids is illustrated for arachidonic acid.
Synthese und Reinheitskontrolle des 1,3,5‐ Trimethyl‐2,4,6‐tris‐(3,5‐di‐tert.‐butyl‐4‐hydroxy‐benzyl‐14C) benzols
Authors: Figge K. 
Published: October 2006

AbstractDie Synthese des markierten Antioxydans 1,3,5‐Trimethyl‐2,4,6‐tris‐ (3,5‐di‐tert.‐butyl‐4‐hydroxy‐benzyl‐14C) benzol und die radiodünnschichtchromatographische Reinheitskontrolle des Zwischenund Endproduktes auf Kieselgel H mit verschiedenen Fließmittelsystemen werden beschrieben. Ausgehend von Paraformaldehyd‐14C und 2,6‐Di‐tert.‐butyl‐phenol über 2,6‐Di‐tert.‐butyl‐4‐hydroxymethyl‐14C‐phenol und anschließende Friedel‐Crafts‐Alkylierung von 1,3,5‐ Trimethylbenzol wird das reine Antioxydans in einer radiochemischen Ausbeute von 47,6 % d. Th., bezogen auf Paraformaldehyd‐14C, und einer chemischen Ausbeute von 49,0 % d.Th., bezogen auf Paraformaldehyd bzw. 2,6‐Di‐tert.‐butyl‐phenol, erhalten. Zwei weitere, radiochemisch einfachere Reaktionswege über das 4‐Cyano‐2,6‐di‐tert.‐butyl‐phenol scheitern an der Einführung der Cyanogruppe; es entsteht als Hauptprodukt das 3,3′,5,5′‐Tetra‐tert.‐butyl‐4,4′‐diphenochinon.
Synthesis of 14C‐labelled 2‐aminothiazole, 2‐amino‐5‐nitrothiazole, 2‐chloro‐5 nitrothiazole, and 1‐(5‐nitro‐2‐thiazolyl)‐2‐imidazolidinone (active substance of ambilhar®)
Authors: Faigle J. W. , Keberle H. 
Published: October 2006

AbstractA description is given of the preparation of 1‐(5‐nitro‐2‐thiazolyl)‐2‐imidazolidinone (active substance of the antiparasitic drug AMBILHAR®) in labelled form. By introducing 14C into the molecule, at position 4 of the imidazolidinone ring in one case and at position 2 of the thiazole ring in the other case, two differently labelled preparations were produced. The specific aetivities were 2.5 mCi/mmole and 0.33 mCi/mmole respectively. As intermediate products and by‐products of the syntheses, three further derivatives of 14C‐thiazole which have not hitherto been described were obtained, i.e. 2‐aminothiazole‐2‐14C, 2‐amino‐5‐nitrothiazole‐2‐14C, and 2‐chloro‐5‐nitrothiazole‐2‐14C.
Synthesis of farnesylacetic acid‐14C and its geraniol ester (Gefarnate‐14C)
Authors: Hazue Masaaki , Miyake Kunio , Endo Michio 
Published: October 2006

AbstractFarnesylacetic acid and its geraniol ester (gefarnate) labelled with 14C at the carbon‐chain were prepared via methyl cyclopropyl ketone‐14C. The intermediate, ketone‐14C was obtained in 63 % radiochemical yield from barium carbonate‐14C and from this ketone‐14C, farnesylacetic acid‐14C and gefarnate‐14C having a specific radioactivity of 1.0 mCi/mmole were prepared in 48.4 % and 37.2 % yield, respectively.
Preparation of 5‐halogeno derivatives of deoxyuridine labelled in the base with 14C
Authors: Filip J. , Nejedly Z. 
Published: October 2006

Abstract5‐Halogeno derivatives of deoxyuridine labelled in the base with 14C were prepared by a single‐step enzymatic synthesis. When using the dicyclohexylammonium salt of 2‐deoxy‐α‐D‐ribose‐1‐phosphate, an enzyme preparation isolated from Escherichia coli B and 5‐halogenouracil‐2‐14C the corresponding deoxyribonucleosides were obtained in a fine yield. The time course of enzymatic reactions and the dependence of yield on concentration of the enzyme preparation and of 2‐deoxy‐α‐D‐ribose‐1‐phosphate were examined. Likewise, the transfer of the deoxyribosyl group between thymidine and 5‐halogenouracil was investigated and it was found that with the reactions studied the reaction equillibrium is approximately independent on type of halogen. For isolating the 5‐halogeno derivatives of deoxyuridine‐2‐14C from the reaction mixture we used preparative paper chromatography and obtained compounds of radiochemical purity exceeding 99 %.
The chemical synthesis of glutamic acid specifically labelled with deuterium or tritium in the alpha or 2 position
Authors: Hochreiter Margaret C. , Schellenberg Karl A. 
Published: October 2006

AbstractGlutamic acid specifically labelled with isotopic hydrogen in the 2 position was produced by exchange equilibration with labelled protons during the reaction of acetylglutamic acid with acetic acid and acetic anhydride. The position of label was established by n.m.r. and mass spectrometry of the deuterium‐labelled compound, and by transaminase‐catalyzed exchange with protons in the case of tritium‐labelled compound. The specific and complete exchange obtained in our experiments contrasts with the previously reported virtual nonlabelling under somewhat different conditions in which the presumed azlactone enolized and hydrolysed in an aqueous medium.
The prospects for stable isotopes. Applications involving nuclear magnetic resonance spectrometry
Authors: Jones J. R. 
Published: October 2006

AbstractRecent developments particularly in the field of nuclear magnetic resonance spectrometry suggest that there is a growing demand for compounds labelled with stable isotopes. In particular the isotopes H2, C13, N15 and O17 offer in some circumstances several advantages over the comparable radioactive isotopes and in this article we show how some workers have grasped the opportunities afforded. The availability of such compounds together with the problems associated with labelling and detection are discussed.
Preparation of riboflavin (UL)‐14C
Authors: Lowry L. K. , Herman Y. F. , Sauberlich H. E. 
Published: October 2006

AbstractUniformly labeled riboflavin‐14C was synthesized by the organism, Ashbya gossypii. Riboflavin with a specific activity of 79.0 mCi/mmole was obtained after extensive purification. Degradation of riboflavin with light and NaOH indicated that the 14C label was present in both the isoalloxazine ring and in the side chain. Radioautographs of the chromatographed vitamin showed that a single radioactive band was found that coincided with authentic riboflavin.
The synthesis and purification of pentylenetetrazole‐10‐14C
Authors: Stiver J. F. , Data J. B. , Christian J. E. 
Published: October 2006

AbstractPentylenetrazole‐10‐14C was synthesized by reacting hydrazoic acid with cyclohexanone‐1‐14C. Purification was carried out using sublimation and thick layer chromatography. Proof of radiochemical purity was determined using thin layer chromatography and autoradiography. The specific activity was found using liquid scintillation counting.
Sur une amélioration de la synthèse de l'acétamino‐2 fluorène 14C‐9
Authors: Nguyen‐Hoang‐Nam  , Hoellinger H. , Herbert M. , Nguyen‐Dat‐Xuong  , Pichat L. 
Published: October 2006

AbstractUne amélioration de la synthèse de l'acétamino‐2 fluorène 14C‐9 est décrite. Le produit marqué est purifié par chromatographie sur colonne d'adsorption‐silicagel. Le rendement radioactif global est de 63 % par rapport à Ba14CO3, activité spécifique : 27 mCi/mM.
Synthesis of β‐sitosterol‐3‐14C
Authors: Otto P. P. H. H. L. , Besemer A. C. , Wientjens W. H. J. M. 
Published: October 2006

AbstractThe synthesis of β‐sitosterol‐3‐14C, specific activity 5 mCi/mM, radiochemical purity ≥98 %, is described. Starting from stigmasterol, the complete synthesis consists of eleven reaction steps. It is based on methods described in the literature. For some of the steps, a considerable improvement in yield has been achieved. The actual labelling step is the condensation of 4‐oxa‐Δ5‐stigmasten‐3‐one with phenyl acetate‐14C in the presence of sodium hydride. β‐Sitosterol‐3‐14C has been obtained with a chemical yield of 23 %, based on 4‐oxa‐Δ5‐stigmasten‐3‐one. The radiochemical yield was 10.3 %. Chemical and radiochemical purities of β‐sitosterol‐3‐14C have been determined by means of thin‐layer chromatography, gas‐liquid chromatography and mass spectrometry.
The synthesis of specifically 14C‐labelled 2,6‐diaminopimelic acid and its higher homologues
Authors: Hanuš J. , Vereš K. 
Published: October 2006

AbstractD,L‐2,6‐Diaminopimelic‐(2‐14C) acid was prepared by alkylation of diethyl acetamidomalonate‐(2‐14C) with 5‐bromo‐N‐phthaloyl‐L‐norvaline methyl ester and hydrolysis of the condensation product. Depending on the alkylation conditions, partial or complete racemisation takes place and therefore the L,L‐form of diaminopimelic acid had to be isolated by paper chromatography. Alkylation of diethyl acetamidomalonate‐(2‐14C) with diethyl 4‐bromobutyl‐ or 5‐bromopentyl‐ or 6‐bromohexylacetamidomalonate and subsequent hydrolysis of the condensation products gave D,L‐2,7‐diamino‐suberic‐(2‐14C), D,L‐2,8‐diaminoazelaic‐2‐14C, and D,L‐2,8‐diaminosebacic‐(2‐14C) acids respectively.
Synthesis of ascorbic‐6‐14C acid
Authors: Karr Dale B. , Baker Eugene M. , Tolbert Bert M. 
Published: October 2006

AbstractL‐ascorbic‐6‐14C acid with a specific activity of 3.25 μCi/mg was prepared from D‐glucose‐1‐14C in an overall yield of 10 %. Synthetic steps were : glucose to sorbitol, sorbose, diisopropylidene sorbose, potassium diisopropylidene 2‐ketogulonate, 2‐ketogulonic acid and ascorbic acid. In a similar manner L‐ascorbic‐5‐14C acid was prepared from D‐glucose‐2‐14C. Conversion of 2‐keto‐L‐gulonic acid to ascorbic acid was done in 0.5 M trifluoroacetic acid solution at 115°C with 2 % acetone as a decomposition inhibitor. The reaction probably proceeds via an enediol intermediate.
32P and 51Cr labelled sodium polyphosphates: Preparation and stability
Authors: Anghileri Leopoldo J. 
Published: October 2006

AbstractThe preparation and stability of 32P and 51Cr labelled sodium polyphosphates have been studied. The influence of the chromium concentration on the solubility of the chromium‐sodium polyphosphate indicates that its effects are more critical in the preparation of the cross‐linked variety. Both polyphosphates showed a very good stability to the storage.
A study of the stability and radiochemical purity of some radiopharmaceuticals. 2. Labelled chlormerodrin
Authors: Buriánek J. , Cífka J. 
Published: October 2006

AbstractThe chromatographic behaviour of chlormerodrin and its radiochemical impurities was studied in various solvents. The main product of thermal decomposition of chlormerodrin was identified as 3‐chloromercuri‐2‐hydroxypropylurea. The thermal decomposition of chlormerodrin is accelerated by the presence of theophylline and suppressed by sodium chloride. The main product of radiation decomposition of chlormerodrin is inorganic mercury. The yield of radiation decomposition was studied as a function of the concentration of chlormerodrin. The radiation decomposition of chlormerodrin is not essentially influenced by the presence of some other substances, however these substances can under certain circumstances support the formation of 3‐chloromercuri‐2‐hydroxypropylurea as the product of the radiolysis.
Synthesis of dexamethasone labeled with carbon‐14 and tritium
Authors: Mertel H. E. , Gerber A. M. , Meriwether H. T. 
Published: October 2006

AbstractThe syntheses of dexamethasone‐16α‐(methyl)‐14C and dexamethasone‐16β‐3H are described. Tritium labeling was achieved by catalytic addition of tritium to 3‐acetoxypregn‐16‐ene‐11,20‐dione, followed by bromination and dehydrobromination to give 3α‐acetoxy‐16‐3H‐pregn‐16‐ene‐11, 20‐dione. The stereochemistry of this sequence of reactions has been studied in detail. Carbon‐14 was introduced into the steroid nucleus by reaction of methyl‐14C‐magnesium iodide with 3α‐acetoxypregn‐16‐ene‐11,20‐dione. These tritium and carbon‐14 labeled intermediates were then carried through to the corresponding labeled dexamethasone by parallel reaction sequences.