Synthesis of 3α-hydroxy-6-ketobrassinosteroids

The synthesis has been effected of the new brassinosteroids (22S,23S)-28-homotyphasterol, 24-epityphasterol, and (22S,23S)-24-epityphasterol, which belong to the 3α-hydroxy-6-oxosteroids. For obtaining (22S,23S)-28-homotyphasterol from stigmasterol, a new scheme of synthesis has been developed the key stages of which are the reduction of a 2α,3α-epoxy-6-ketone with lithium tetrahydroaluminate and the selective oxidation of the resulting 3α,6β-diol to the 3α-hydroxy-6-ketone.     

A novel scalable and stereospecific synthesis of 3α- and 3β-amino-5α-androstan-17-ones and 3α- and 3β-amino-5α-pregnan-20-ones

A novel scalable stereoselective synthesis of 3α- and 3β-amino-5α-androstan-17-ones and 3α- and 3β-amino-5α-pregnan-20-ones has been developed using phthalimide based Mitsunobu chemistry. In all four cases, the products were isolated as single diastereoisomers in high chemical yield and purity without the need for chromatography at any stage in their syntheses.     

The synthesis of a series of (α-amino)indol-3-yl ketones

A series of [(α-amino)indol-3-yl]-2-methyl-1-propanones and [(α-amino)indol-3-yl]cyclopentylmethanones has been synthesized by a variety of reductive reactions performed on the corresponding series of (α-azido)-indol-3-yl ketones. One of the more interesting reductive procedures involved the palladium-catalyzed decomposition of formic acid with the formation of hydrogen in situ. The (α-azido)ketones were prepared in excellent yield by the displacement of the tertiary bromine atom from the (α-bromo)ketones using sodium azide in N,N-dimethylformamide. Bromination was accomplished by using either cupric bromide in ethyl acetate/chloroform or phenyltrimethylammonium tribromide in tetrahydrofuran.     

Synthesis and conformational analysis of isomeric 3-propananilidotropanes

The isomeric 3-anilino and 3-propananilidotropanes have been synthesized and obtained in isomerically pure form. The configurations and solute conformations of these isomers were studied via glc and nrar analysis. The 3β-isomers have been shown to exist in the normal piper-idine chair conformation whereas the 3α-anilino tropane exists in a flattened piperidine chair conformation and the 3α-propananilidotropane isomer preferentially exists in a conformation in which the piperidine ring system is a boat.     

Convenient stereoselective synthesis of some 3-aminosteroid scaffolds

Abstract

An efficient stereoselective synthesis 3α- and 3β-aminoandrostan-17-one and 3α-amino dehydroepiandrosten-17-one based on a Mitsunobu reaction has been developed, using azide as the ammonia equivalent. All the products were isolated in high yield.     

Synthesis of all 7αH-guaia-4,11-dien-3-one diastereomers from (+)-dihydrocarvone

All four 7αH-guaia-4,11-dien-3-one diastereomers have been synthesized from the common intermediate 1αH,10α-acetoxy-7αH-guaia-4,11-dien-3-one obtained from (+)-dihydrocarvone. The spectral features of the four diasteromers have been correlated and the structure and absolute configuration of 1βH,10βH,7αH-guaia-4,11-dien-3-one isolated from Pleocarphus revolutus has been confirmed.     

A synthesis of 3α-dihydrocadambine

3α-Dihydrocadambine has been synthesized from secologanin.     

Synthesis and transformations of (±)-trans-4aβ(H), saα(H)-octahydro-4α,7β-dimethyl-2H-1-benzopyran-2-one

Hydrogenation of 4,7-dimethylcoumarin ( 1 ) in alkaline medium has been shown to furnish a mixture of (±)-trans-4aβ(H),8aα(H)-octahydro-4α,7β-dimethyl-2H-1-benzopyran-2-one ( 2 ), (±)-trans-4aβ(H),8aα(H)-octahydro-4α,7α-dimethyl-2H-1-benzopyran-2-one ( 3 ) and (±)-cis-4aα(H),8aα(H)-octahydro-4α,7α-dimethyl-2H-1-benzopyran-2-one ( 4 ) in 40:25:35:ratio, respectively. The stereochemistry of the major hydrogenation product 2 , has been established by transforming it to p-menthane derivatives e.g. (±)-2 (R)-[2′(R)hydroxy-4′(R) methylcyclohex-(1′S)-yl]propan-1-ol ( 20 ) and (±)-trans-3α,6β-dimethyl-3aβ(H),7aα(H)-octahydrobenzofuran ( 12 ). Starting from a mixture of lactones 2, 3 and 4 , lactone 3 has been obtained in pure state employing a sequence of reactions.     

Synthesis of Methyl 2-Acetamido-4,6-di-O-acetyl-3-S-acetyl-2-deoxy-3-thio-α-D-mannopyranoside

Methyl-2-acetamido-4,6-di-O-acetyl-3-S-acetyl-2-deoxy-3-thio-α-D-mannopy-ranoside has been synthesized by conversion of methyl 2-amino-2-deoxy-4,6-O-benzylidene-α-D-altropyranoside into the corresponding 3-O-methanesulfony1-2-N-[(methylthio)thiocarbonyl]derivative followed by intramolecular displacement of the 3-O-methanesulfonyloxy group with the (methylthio)thiocarbamoyl group.     

The ‘Azirine/Oxazolone Method’ on Solid Phase: Introduction of Various α,α‐Disubstituted α‐Amino Acids

Peptides containing various α,α‐disubstituted α‐amino acids, such as α‐aminoisobutyric acid (Aib), 1‐aminocyclopentane‐1‐carboxylic acid, α‐methylphenylalanine, and 3‐amino‐3,4,5,6‐tetrahydro‐2H‐pyran‐3‐carboxylic acid have been synthesized from the N‐ to the C‐terminus by the ‘azirine/oxazolone method’ under solid‐phase conditions. In this convenient method for the synthesis of sterically demanding peptides on solid‐phase, 2H‐azirin‐3‐amines are used to introduce the α,α‐disubstituted α‐amino acids without the need for additional reagents. Furthermore, the synthesis of poly(Aib) sequences has been explored.     

First Total Synthesis of 3α,4α-Oxidoagarofuran and (-)-3β,4α-Dihydroxy-β-dihydroagarofuran

The first stereoselective total synthesis of (–)-3β, 4α-dihydroxy-β-dihydroagarofuran (1) and 3α, 4α-oxidoagarofuran (2) has been described. The key step is the epoxidation of α-agarofuran (6) with dimethyldioxirane.     

An efficient method for the synthesis of methyl 11α-amino-3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate

The synthesis of methyl 11α-azido-3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate, methyl 11β-azido-3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate and methyl 11α-amino-3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate have been achieved. Mechanistic aspects for the decomposition of steroidal azidoketones to its enamines are discussed.     

Synthesis and biological evaluation of 3-beta,20(R)-dihydroxy-protost-24-ene

The possible lanosterol precursor, 3β, 20(R)-dihydroxy-protost-24-ene ( 1 a ) has been prepared, in thirteen steps, from 3α-hydroxy-4α, 8, 14-trimethyl-18-nor-5α, 8α, 9β, 13ξ, 14β-androstan-17-one (mixture of 2 and 3 ). In vitro experiments with rat liver homogenates failed to convert 1 a to lanosterol.     

226. Aminonucleosides. 3. Derivatives of 3-amino-3,5-dideoxy-D-lyxo- and D-ribo-pentoses

The 3-amino-3,5-didesoxy-1,2-O-isopropylidene-α-D -ribofuranose and -β-D -lyxo-furanose and several derivatives thereof have been prepared by hydride reduction of the corresponding oximes.     

Ring-opening copolymerization of α-chloromethyl-α-methyl-β-propionolactone with ε-caprolactone

α-Chloromethyl-α-methyl-β-propionolactone (CMMPL) has been copolymerized with ε-caprolactone (CL) using a wide range of feed compositions and aluminium triisopropoxide [Al(OⁱPr)₃] as an initiator. Random copolymers of CMMPL with CL were obtained. The pendant chloromethyl groups of the copolymer were converted to quaternary ammonium salts by reaction with pyridine, resulting in an increased hydrophilicity of the copolymers.     

Culcitosides C2 and C3 from the starfishCulcita novaeguineae

Two steroid glycosides not previously described have been isolated from the digestive system of the starfishCulcite novaeguiniae, and these have been called culcitosides C₂ and C₃. With the aid of chemical and spectral methods, the chemical structure of C₂ has been established as 24ξ-methyl-5α-cholestane-3β,4β,6α,8,15β,16β,28-heptaol 28-O-[O-(2,4-di-O-methyl-β-D-xylopyranosyl)-(1 → 2)-α-L-arabinofuranoside, and that of C₃ as its 4-deoxy analogue.     

Syntheses of 3-Deoxy-3-Fluoroglucosamine Derivatives

ABSTRACT

Methyl

2-acetamido-4,6-di-0-acetyl-2,3-dideoxy-3-fluoro-α-D-glucopyranoside (5) and methyl 2-diallylamino-2,3,6-trideoxy-3,6-difluoro-4-0-methanesulfonyl-α-D-glucopyranoside (10) were prepared from methyl 4,6-0-benzylidene-α-D-glucopyranoside. Fluorination at C-3 was carried out by ring opening of an aziridinium ion. Two fluorinating reagents were used depending on the starting material.     

Iodine-mediated direct synthesis of 3-iodoflavones

Molecular iodine has been used for the regioselective, one pot, direct synthesis of 3-iodoflavones from 2′-allyloxy chalcones, 2′-hydroxy chalcones and flavones. Allyl deprotection, cyclization dehydrogenation and α-iodination of 2′-allyloxychalcones has been achieved in a single step to offer 3-iodoflavones.     

Synthese und IR.-spektroskopische Identifizierung epimerer 3-Äthinyl-5 α-cholestan-3-ole

Synthesis and IR. Spectroscopic Identification of Epimeric 3-Ethinyl-5α-cholestan-3-ols The syntheses of the 3β-ethinyl-5α-cholestan-3α-ols 2a, 2b, 2c and of the corresponding epimeric 3α-ethinyl-5 α-cholestan-3 β-ols 3a, 3b, 3c are described. Bands at 1000 cm^?1 for the α-alcohols and at 1030 cm^?1 for the β-alcohols are found to be useful for the IR. spectroscopic identification of epimeric 3-ethinyl-5α-cholestan-3-ols.     

Acylation of steroid alcohols with 3-carboxypropanamido acids

Chemistry of Natural Compounds - Using N-(3-carboxypropanoyl)-β-phenyl-α-alanine as a model it has been established that when steroid alcohols are esterified with 3-carboxypropanamido...