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.     

Diastereoselective synthesis of N-acetyl-D,L-acosamine and N-benzoyl-D,L-ristosamine

N-Acyl derivatives of $\text{D}$,$\text{L}$-acosamine and $\text{D}$,$\text{L}$-ristosamine were synthesized with high stereo selectivity utilizing intramolecular Michael addition of γ- and δ-carbomoyloxy-α,β-unsaturated esters.     

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     

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.     

Stereoselective synthesis of (25R)-25,26-dihydroxy-23-oxovitamin D3 and its enzymatic conversion to (25R)-1α,25,26-trihydroxy-23-oxovitamin D3, a putative metabolite of vitamin D3

(25$\text{R}$)-25,26-Dihydroxy-23-oxovitamin D₃ was synthesized efficiently and stereoselectively, and it was converted enzymatically to (25$\text{R}$)-1α,25,26-trihydroxy-23-oxovitamin D₃, a putative metabolite of 1α,25-dihydroxyvitamin D₃. The spectral and chemical properties of (25$\text{R}$)-25,26-dihydroxy-23-oxovitamin D₃ and its 1α,hydroxylated derivative disagree with those reported for the isolated metabolite.     

Reversal of diastereofacial selectivity in the intramolecular michael addition of -α-carbamoyloxy-α,β-unsaturated esters. Synthesis of N-benzoyl-D,L-daunosamine

Contrary to the precedents, 1,3-anti stereoselection was found in the intramolecular Michael addition of ethyl $\text{threo}$,5-carbamoyloxy-4-trialkylsilyloxy-2-hexenoate to culminate in a synthesis of N-benzoyl-$\text{D}$,$\text{L}$-daunosomine. The antiperiplanar effect due to the group at 4-position was revealed to play a major role in the stereoselection in this type of reactions. N-benzoyl-$\text{D}$,$\text{L}$-3-epidaunosamine was also synthesized by 1,2-syn asymmetric induction.     

The B&.sbnd;X (3500 Å) transition of azulene: Medium-dependent effects attributable to vibronic coupling and vibronic Fermi resonance

The vibrational structure of the absorption spectrum of azulene near 3500 Å (to the second excited singlet state, $\text{B}$ is markedly altered by changing the molecular environment, even though the corresponding emission spectrum remains largely unchanged. The interpretation proposed invokes vibronic coupling sufficiently strong (i) to effect large changes in the vibrational energy levels of state $\text{B}$, (ii) to couple vibronically active modes to each other, and (iii) to induce resonances with most two-quantum states of the right symmetry. The coupling is to a higher state $\text{D}$, and the effects to different media attributed to modifications of the energy gap between the $\text{B}$ and $\text{D}$ states.     

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 N-benzoyl-L-daunosamine from D-threonine

The synthesis of N-benzoyl-$\text{L}$-daunosamine (14) from the C₄$\text{threo}$ aldehyde (2b), prepared from $\text{D}$-threonine, through the intermediacy of the C₇ adduct (7a) is reported     

A short synthesis of (s)-5-hydroxymethyl-(5h)-furan-2-one and derivatives from d-ribonolactone

We describe a short synthesis of ($\text{S}$)-5-hydroxymethyl-(5$\text{H}$-furan-2-one and some 5-O-derivatives, which are being used as key starting products for the synthesis of several antileukaemic lignan lactones, from $\text{D}$-ribonolactone.     

Use of 13C spin-lattice relaxation measurements to determine the structure of a tetrabromo diphenyl ether from the sponge Dysideaherbacea

The structure of a novel tetrabromodiphenyl ether from $\text{D}$. $\text{herbacea}$ is solved principally by analysis of the contributions of non-bonded hydrogens to the spin-lattice relaxation times of quaternary carbons.     

Synthesis of 26,26,26-trifluoro-25-hydroxy and 27-nor-26,26,26-trifluoro-25-hydroxyvitamin D3

Two new fluorinated 25-hydroxyvitamin D₃ analogs, 26,26,26-trifluoro- 25-hydroxy ($\text{1}$) and 27-nor-26,26,26-trifluoro-25-hydroxyvitamin D₃ ($\text{2}$), were prepared from 24-phenylsulfonyl 25,26,27-triorcholest-5-en-3β-yl tetrahydropyranyl ether ($\text{3}$).     

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.     

Synthesis of the serine equivalent, (2R) and (2S)-amino-3-butenol derivatives. Synthetic approaches to the metal chelating poly-amino acid, “aspergillomarasmine A”

Chiral synthons, equivalent to the C₃ amino acid serine, were synthesized in both (2$\text{R}$) and (2$\text{S}$) form from $\text{D}$ or $\text{L}$-methionine respectively; Utilization of this synthon in the construction of metal chelating poly-amino acid aspergillomarasminea A skeleton is presented.     

Sugar chemistry without protecting groups: a novel regioselective synthesis of 6-O-acyl-D-glucopyranoses and methyl-6-O-acyl-α-D-glucopyranosides

The primary hydroxyl groups of α-$\text{D}$-glucose and methyl-α-$\text{D}$-glucoside were selectively esterified by treating the free sugars with $\text{N}$-acylthiazolidine-2-thiones, thus affording respectively 6-$\text{O}$-acyl-$\text{D}$-glucopyranoses and methyl-6-$\text{O}$-acyl-α-$\text{D}$-glucopyranosides in high yields. This new reaction is compared with our previous synthesis of 1-$\text{O}$-acyl-β-$\text{D}$-glucopyranoses from β-$\text{D}$-glucose and interpreted in terms of anomeric effect.     

A stereocontrolled partial synthesis of 1α-hydroxy vitamin D3

A novel and efficient partial synthesis of 1α-hydroxy vitamin D₃ ($\text{6}$), starting from 7-dehydrocholesterol ($\text{1}$), is reported. The crucial step in the synthesis involves a selective Diels-Alder reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with the 6,8-diene system of previtamin D₃ ($\text{3}$), generating an adduct $\text{7}$ suitable for the stereoselective introduction of the 1α-hydroxyl group. Cycloreversion of $\text{13}$ leads to the title compound.     

Application of 13C N.M.R. in a re-examination of the isopropylidenation of D-ribose diethyldithioacetal and erythritol

The di-$\text{O}$-isopropylidene acetals resulting from the reaction of $\text{D}$-ribose diethyldithioacetal and erythritol with acidic acetone have been shown to contain 5- and 7- but not 6-membered rings.     

Molecular predissociation dynamics revealed through multiphoton ionisation spectroscopy. I. The C1B1 states of H2O and D2O

The $\text{C}$¹B₁ states of H₂O and D₂O have been observed by means of three photon absorption (four photon ionisation) spectroscopy. Differences between the experimentally observed 3 + 1 multiphoton ionisation spectrum and that predicted by the appropriate asymmetric-top three-photon line-strength theory are attributed to $\text{C}$ state predissociation. Two separate predissociation mechanisms have been identified, one (heterogeneous) relying on a-axis parent molecular rotation to couple the bound B₁ state to an unbound state of A₁ electronic symmetry, the other (homogeneous) involving a second, dissociative excited electronic state of B₁ symmetry. Having established the detailed $\text{C}$ state predissociation dynamics, two photon absorption spectra of H₂O and D₂O ($\text{C}$ ← $\text{X}$) can be predicted accurately: studies of individual quantum-state-selected photofragmentation processes from H₂O($\text{C}$) are proposed.     

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.     

Synthesis of 2β-fluoro-1α-hydroxyvitamin D3

2β-Fluoro-1α-hydroxyvitamin D₃($\text{3}$) was prepared from 1,2α-epoxy-cholest-5-en-3β-yl tetrahydropyranyl ether($\text{1a}$ via 2β-fluorocholest-5-ene-1α, 3β-diol($\text{2}$).