Cyanosugars III : The reaction of trimethylsilyl cyanide with keto,epoxy and acetal derivatives of carbohydrates

Reaction of methyl 2-acetamido-4,6-$\text{O}$-benzylidene-2-deoxy-α-$\text{D}$-$\text{ribo}$-hexopyranosid-3-ulose with Me₃SiCN afforded methyl 2-acetamido-4,6-$\text{O}$-benzylidene-3-$\text{C}$-cyano-2-deoxy-3-$\text{O}$-trimethylsilyl-α-$\text{D}$-$\text{allo}$- Reaction of ethyl 4,6-di-$\text{O}$-acetyl-2,3-anhydro-α-$\text{D}$-mannopyranoside with Me₃SiCN gave the corresponding ethyl 4,6-di-$\text{O}$-acetyl-2-$\text{C}$-cyano-2-deoxy-α-$\text{D}$-glucopyranoside. Reaction of methyl 4,6-$\text{O}$-benzylidene-2,3-anhydro-α-$\text{D}$-allopyranoside or methyl 4,6-$\text{O}$-benzylidene-2,3-di-$\text{O}$-tosyl-α-$\text{D}$-glucopyranoside with Me₃SiCN at - 75° or - 50° gave the corresponding methyl 6-$\text{O}$-[(R)-cyano phenyl methyl]-α-$\text{D}$-glyco-pyranosides with high or total regio and stereoselectivity.     

A new method for the synthesis of some 9-β-D-arabinofuranosylpurines by a combination of chemical and enzymatic reactions

An enzymatic transarabinosylation between 2-chlorohypoxanthine and 1-β-$\text{D}$-arabinofuranosyluracil gave 9-β-$\text{D}$-arabinofuranosyl-2-chlorohypoxanthine which was chemically converted to 9-β-$\text{D}$-arabinofuranosylguanine and its derivatives.     

13C-NMR spectra of 6-aminohexyl glycosides of O-β-D-galactopyranosyl-2-acetamido-2-deoxy-β-D-glucopyranose

¹³C-NMR spectral data on 6-aminohexyl glycosides of $\text{O}$-β-$\text{D}$-galactopyranosyl-2-acetamido-2-deoxy-β-$\text{D}$-glucopyranose are pr     

A synthesis of β-2′-deoxyshowdomycin

A stereospecific synthesis of the 2′-deoxy analogue of showdomycin, 2-(2′-deoxy-β-$\text{D}$-ribofuranosyl)-maleimide, from 2,5-anhydro-$\text{D}$-glucitol is described.     

Total synthesis of the disaccharide of bleomycin, 2-0-(α-D-mannopyranosyl)-L-gulopyranose

2-0-(α-$\text{D}$-Mannopyranosyl)-$\text{L}$-gulopyranose, the sugar portion of bleomycin has been synthesized.     

Synthesis of β-d-mannopyranosides and regioselective o-alkylation of dibutylstannylene complexes

Alkylation of dibutylstannylene complexes of 3,4,6-tri-$\text{O}$-benzyl-$\text{D}$-mannopyranose, methyl 6-$\text{O}$-trityl-α-$\text{D}$-mannopyranoside and methyl α-$\text{D}$-mannopyranoside gives respectively β-$\text{D}$-mannopyranoside and 3-$\text{O}$-alkyl derivatives with high selectivity.     

Conformational dependence of pyranoid rings 1,2-cis-fused to dioxolane rings on the configuration of the dioxolane rings in acetylated derivati

X-Ray and ¹H N.M.R. studies on pyranoid rings 1,2-$\text{cis}$-fused to dioxolane rings in acetylated $\text{D}$-gluco- and $\text{D}$--galactopyranose derivatives demonstrate that the configuration of the dioxolane ring influences the conformation of the pyranoid ring in the $\text{D}$-gluco but not in the $\text{D}$-galactopyranose series. The crystal structure of 3,4,6-tri-$\text{O}$-acetyl-1,2-$\text{O}$-(R)--(l-cyano-ethylidene)-α-$\text{D}$-glucopyranose ($\text{1}$) and 3,4,6-tri-$\text{O}$-acetyl-1,2-$\text{O}$-($\text{R}$)-(1-cyano-ethylidene)-α-$\text{D}$-galactopyranose ($\text{2}$)have been determined by X-ray analysis. Lattice parameters for $\text{1}$ are a=20.6021 (11), b=8.0438 (2), c=5.5541 (1) Å and β= 95.588 (3)° for a cell with P21 symmetry. These parameters for $\text{2}$ are a=20.3361 (7), b=10.0907 (2), c=18.9115 (5) Å, β =112.399 (2)°, C2, with two crystallographycally independent molecules. The conformation of the pyranoid ring in both compounds can be described as flattened ⁴C₁ and that of the dioxolane ring as distorted E₁. The importance of the torsion angles for describing problems of configuration is remarked and the use of relative configurational angles is stressed. The ¹H N.M.R. spectra of $\text{1}$ and $\text{2}$ and 3,4,6-tri-$\text{O}$-acetyl-1,2-O-(S)- and (R)-ethylidene-α-$\text{D}$-glucopyranose ($\text{5}$ and $\text{7}$), 3,4,6-tri-O-acetyl--1,2-O-(S)- and ($\text{R}$)-ethylidene-α-$\text{D}$-galactopyranose ($\text{6}$ and $\text{8}$), and 3,4,6-tri-$\text{O}$-acetyl-1,2-$\text{O}$-($\text{S}$)-and ($\text{R}$)-benzylidene-α-$\text{D}$-glucopyranose ($\text{9}$ and $\text{10}$) have been analyzed by using iterative computer methods and N.O.E. measurements. The results indicate that the major solution conformation of the pyranoid ring of the derivatives in the $\text{D}$-gluco series $\text{1}$, $\text{5}$ and $\text{9}$ may be described as flattened ⁴C₁ and that of $\text{7}$ and $\text{10}$ as ²$\text{S}$₅. The major solution conformation of the pyranoid ring in all compounds in the $\text{D}$-galacto series ($\text{2}$,$\text{4}$,$\text{6}$,$\text{8}$) may be described as flattened ⁴$\text{C}$₁.     

A case of oligomerization on attempted chlorination of an α-hydroxy acetal with the triphenylphosphine tetrachloromethane reagent

Treatment of methyl 3,5-dideoxy-β-$\text{D}$-$\text{erythro}$-pentofuranoside $\text{8}$ with the Ph₃P-CCl₄ reagent gave none of the expected 2-chloro derivative but a mixture of l→2 linked oligosaccharides, $\text{9}$, $\text{10}$ with some higher homologues, terminated by αa 2-chloro-2,3,5-trideoxy-α-$\text{D}$-$\text{threo}$-pentofuranosyl unit at the non reducing end.     

Stereochemistry of nucleophilic addition reactions 13 : Kinetically controlled nucleophilic addition reactions to methyl 4,6-0-benzylidene-2,3- dideoxy-2-nitro-β-D-erythro-hex-2-enopyranoside: an important role of a(1,3) strain

An improved synthesis of methyl 4,6-0-benzylidene-2,3-dideoxy-2-nitro-β-D-erythro-hex-2-enopyranoside and its reactions with various nucleophiles are described; all the nucleophiles were found to approach exclusively or predominantly from the equatorial side of the molecule, giving the β-D-glucopyranoside derivatives as the major or exclusive product. The stereochemical course of approach of a nucleophile observed in the present reactions and in the literature are discussed.     

A novel and efficient synthesis of the naturally occurring nucleoside doridosine

1-Methylisoguanosine was synthesized by a one-pot reaction involving a condensation of 5-amino-1-(β-$\text{D}$-ribofuranosyl)imidazole-4-carboxamide (1) with methyl isothiocyanate, treatment of the resulting thiourea derivative with DCC furnished 5-(3-methyl-1-ureido)-1-(β-$\text{D}$-ribofuranosyl)imidazole-4-carbonitrile (4) which was then annulated with ethanolic ammonia to furnish doridosine in a 68% yield from 1.     

Synthesis of “9-deazaadenosine”; A new cytotoxic C-nucleoside isostere of adenosine

The synthesis of 7-(β-$\text{D}$-ribofuranosyl)-4-amino-5H-pyrrolo[3,2-$\text{d}$]pyrimidine (9-deazaadenosine) $\text{9}$ is described. It involves base-catalyzed cyclization of N-carboethoxyenamine $\text{4}$ to give β- and α-ribosylated 3-amino-2-cyanopyrroles $\text{6}$ and $\text{7}$, respectively, followed by a one-step conversion to the desired pyrrolo[3,2-$\text{d}$]pyrimidine system.     

Mevinic acids and analogues: preparation of a key chiral intermediate

The preparation of methyl 3-0-tert-butyldiphenylsilyl-2,4-dideoxy-β-$\text{D}$-$\text{erythro}$- hexopyranoside, a key chiral intermediate for mevinic acids, and its elaboration into four mevinate analogues are described.     

The invention of new radical chain reactions. part X: High yield radical addition reactions of αβ-unsaturated nitroolefins. An expedient construction of the 25-hydroxy-vitamin D3 side chain from bi

Radicals derived from thiohydroxamic esters $\text{3}$ readily add to nitroolefins $\text{5}$ (Z = NO₂) to give good yields of α-nitrosulphides. These adducts, where the structure permits, are easily oxidised to carboxylic acids $\text{8}$ by treatment with alkaline hydrogen peroxide. Reductive cleavage to the corresponding aldehydes or ketones $\text{9}$ is efficiently carried out by the action of TiCl₃. Addition of methyl magnesium iodide to the methyl ketone derived from 3α-acetoxy 11-oxo cholanic acid gives steroid $\text{10}$ possessing the 25-hydroxycholesterol side chain of the vitamin D₃ metabotites. Radical additions to 1-phenylthio-2-nitropropene $\text{11}$ have been briefly studied.     

Synthesis with immobilized enzymes of two trisaccharides,one of them active as the determinant of a stage antigen.

Glycosidation of disaccharides I and III with a system of five immobilized enzymes gave excellent yields of trisaccharides $\text{β-D}$-Gal-(1→4)-$\text{β-D}$-GlcNAc-(1→6)-$\text{D}$-Gal ¦ the I(Ma) determinant ¦ and $\text{β-D}$-Gal-(1→4)-$\text{β-D}$-Glc-NAc-(1→3)-$\text{D}$-Gal, on the milimole scale.     

N-nitrosothialdine. Synthesis,X-ray crystallography,and N-N rotational barrier

Crystalline N-nitrosothialdine ($\text{2}$) has been prepared in 38% yield by treating thialdine ($\text{1}$) with $\text{n}$-butyl nitrite and acetic acid in hexane. X-Ray crystallography of $\text{2}$ revealed that its three methyl groups are a11 $\text{cis}$ and, rather surprisingly, all equatorial; this finding contrasts sharply with results for other nitrosamine heterocycles which have been investigated, whose bulky alpha substituents are forced into a primarily axial orientation by the large steric requirement of the N-N-0 system. The equatorial methyl group both displaces the nitroso group from the C-N-C plane and twists it somewhat about the N-N bond. N-Nitrosothialdine's unusually low barrier to rotation about the N-N bond (72 kJ/mole) is attributed to this steric crowding, combined with inductive electron withdrawal by the two sulfur atoms.     

Synthese von oligosaccharid-determinanten des T-antigens mit amid-spacer zur darstellung synthetischer antigene

The β (1 → 3) -linked disaccharide $\text{1}$$\text{5}$ was synthesized from $\text{D}$-galactose and a $\text{D}$-galactosamine unit with a watersoluble amide spacer. This represents the hapten of T-antigen and, when coupled to a protein, is suitable for use as an artificial antigen. Other O-β-$\text{D}$-galactosylated derivatives of galactosamine were synthesized.     

Boat-chair conformational preference of exo, exo-9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid

The ¹H and ¹³C nmr spectra of $\text{exo}$, $\text{exo}$-9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid, 3, in DMSO-d₆ or alkaline D₂O, clearly show that it exists in a $\text{boat}$-$\text{chair}$-conformation with $\text{equatorial}$ carboxyl groups, thus being the first case of $\text{boat}$-$\text{chair}$ preference of a bicyclo[3.3.1] nonan-9-one due to the presence of $\text{exo}$,$\text{exo}$-2,4- substituents.     

12-S-CIS conformationally locked retinoids: Thermal and photochemical interconversions leading to new geometric isomers

For 12-$\text{s}$-$\text{cis}$ locked retinal analogues, thermal equilibria are established between 11-$\text{cis}$, 13-$\text{cis}$-1c and 13-$\text{cis}$-2c and between 9-$\text{cis}$, 11-$\text{cis}$, 13-$\text{cis}$-1d and 9-$\text{cis}$, 13-$\text{cis}$-2d; a photoisomerization occurs to transform 2c to $\text{all}$-$\text{trans}$-2a and 2d to 9-$\text{cis}$-2b     

Conformation,in solution,of c-4-t-butyl-1-phenyl-r-1-(N-piperidyl)cyclohexane hydrochloride. The conformational energy of t-butyl

Although the hydrochloride of $\text{c}$-4-$\text{t}$-butyl-1-phenyl-$\text{c}$-1-(N-piperidyl)cyclohexane crystallizes in the conformation with axial $\text{t}$-butyl, it exists as an almost equimolar mixture of the two chair conformers in CD₂ Cl₂ solution. The position of equilibrium allows one to calculate ΔG°_{$\text{t}$-Bu} as ?4.9 kcal/mol.     

Cis - oxyamination routes to amimo sugars: A simple synthesis of holacosamine

The known D-$\text{threo}$ hex-2-enopyranoside $\text{1a}$ is converted into an N-methyl allyl amine, the methyl urethane of which undergoes electrophile-induced cyclisation to give the iodocyclic urethane $\text{9}$. The $\text{cis}$ relationship of H3 and H4 in the latter is confirmed by NMR spectroscopy. Reduction at C2 and C6 is done simultaneously and the cyclic urethane is hydrolysed. The amino group is then acetylated and the hydroxy group methylated.