Synthesis of both the enantiomers of sclerosporin and sclerosporal,sporogenic substance of sclerotinia fructicola1

Both the enantiomers of sclerosporin $\text{1}$ and sclerosporal $\text{2}$ were synthesized from (-)-carvone. (4R,9R,10S)-(+)-Sclerosporin and (4R,9R,10S)-(-)-sclerosporal were identified as the natural enantiomers by a comparison of their CD-spectra. An intramolecular Diels-Alder route was proved to be an efficient method of preparing sufficient amounts of (+)-$\text{1}$ for the biological study.     

The octant rule. XIV. synthesis and circular dichroism of α-exo and endo-deuteriobicyclo[3.2.1]octan-3-one and 6,6-dimethybicyclo[3.1.1]heptan-3-one

(1R,5S)-2S-Deuteriobicyclo[3.2.1]octan-3-one ($\text{1}$) and (1R,5S)-2R-Deuteriobicyclo[3.2.1]octan-3-one ($\text{2}$), prepared by diazomethane ring enlargement of (1S,4R)-2(exo)-deuteriobicyclo-[2.2.1] heptan-2-one and (1S,4R)-2(endo)-deuteriobicyclo[2.2.1]heptan-2-one respectively, both gave (?) n-π^* circular dichroism (CD) Cotton effects, Δε^max₂₉₄ = ?0.05 and Δε^max₂₉₄=?0.1, respectively, in hydrocarbon solvent. (1S,5R)-2S-Deuterio-6,6-diaethylbicyclo[3.1.1] heptan-3-one ($\text{3}$) and (1S,5R)-2R-deuterio-6,6-dimethylbicyclo[3.1.1] heptan-3-one ($\text{4}$), prepared from (-) myrtenal, both exhibited extraordinary vibrational fine structure for the n-π^* CD transitions observed in hydrocarbon solvent and oppositely?signed CEs, Δε^max₂₈₂=?0.01 and Δε^max₂₇₉=+0.01 respectively in CF₃CH₂OH solvent.     

Chiral aminoacid containing macrocycles

Optically active macrocycles (R, R)-$\text{8}$-$\text{10}$ and diastereomeric mixtures of (±)-$\text{8}$-$\text{10}$ and meso-(R, S)-$\text{8}$-$\text{10}$ were prepared containing two (R)- or (S)-α-phenylglycine units as sources of chirality.     

High asymmetric induction in diels-alder additions of cyclopentadiene to acrylates derived from isoborneol

Starting from (R)-(+)- and from (S)-(?)-camphor the chiral alcohols $\text{1}$, $\text{2}$ and $\text{3}$ have been prepared; their acrylates II underwent TiCl₂(OR)₂-promoted Diels-Alder additions to cyclopentadiene giving efficiently in a predictable manner either the (2R)- or the (2S)-adducts III with up to virtually quantitative asymmetric induction.     

Calozeylanic acid,a new bark acid from three calophyllum species (guttiferae)

Calozeylanic acid has been isolated from the bark of three $\text{calophyllum}$ species: $\text{C.lankaensis}$ (= $\text{C.zeylanicum}$), $\text{C.thwaitesii}$ and $\text{C.walkeri}$. Its structure has been established as 2(R),3(R)-2,3-Dimetyl- 5-hydroxy-6-(3-methylbutanyl)-6-(3,7-dimethylocta-3,6-dienyl)-7-oxo-8- (2-carboxy-1-phenylethyl)-2,3,6,7-tetrahydrobenzo-4-pyrone.     

Synthesis of 13C and 15N labelled (S)-Tryptophan

(R,S)-serine-1-¹³C was incubated in a culture of $\text{Escherichia}$$\text{coli}$ cells to produce (S)-trytophan-1-¹³C. Bromoacetyl bromide-2-¹³C was converted to bromoacetanilide and cyclization of the anilide, followed by reduction and dehydrogenation furnished indole-3-¹³C. Indole-¹⁵N was synthesized by known sequences. These ¹³C and ¹⁵N isotomers of indole were converted by commercially available, lyophilized $\text{E}$. $\text{coli}$ to furnish (S)-tryptophan-γ-¹³C and (S)-tryptophan-indole-¹⁵N, respectively.     

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.     

Studies directed towards the asymmetric total synthesis of antileukemic lignan lactones. Synthesis of optically pure key intermediate and its utility

By the self-immolative asymmetric synthesis, optically pure key intermediate β-piperonyl-γ-lactone (R)-(+)-$\text{6}$ was found to be prepared in reasonable yield from the easily available chiral γ-lactone synthon ($\text{1}$) which had been also reported to give an antipode (S)-(-)-$\text{6}$. The optically pure (R)-(+)-$\text{6}$ was shown to be converted successfully into several optically pure natural lignan lactones.     

Carbenoids. Metal assisted ionization

Treatment of (S)-(+)-1-chloro-2,2-diphenylcyclopropane with n-butyllithium at ?25°C yield, $\text{inter}$$\text{alia}$, (R)-(?)-1-$\text{n}$-butyl-2, 2-diphenylcyclopropane with overall inverted configuration. A metal assisted ionization mechanism is proposed.     

Highly stereocontrolled substitution of phenols with pyruvic esters. A viable route to ortho-hydroxyatrolactic esters of (2R)- and (2S)-configuration

Treatment of phenols with optically active (+)- and (?)-menthyl pyruvate assisted by Al(III)- or Ti(IV)-based promoters leads to the formation of $\text{ortho}$-hydroxyatrolactic esters of (2R)- and (2S)-configuration. The use of suitable menthol-based promoters augments markedly (up to 96% d.e.) the intrinsic stereochemical bias of the chiral pyruvate.     

The occurrence of (S)-(−)-squalene-2,3-epoxide in nature: Isolation from the green alga Caulerpa prolifera

The unprecedented isolation of (S)-(?)-squalene-2,3-epoxide (1) from a natural source (green alga $\text{Caulerpa prolifera}$) is reported.     

Crahamimycin A1 synthesis and determination of configuration and chirality

The two hydroxyacid derivatives $\text{10}$ and $\text{11}$, obtained from (S)-β-hydroxybutanoate and (S)-lactate, respectively, are joined to give the acetylenic ester $\text{12}$. Cyclization and functional group manipulations lead to (S,S)-(+)-grahamimycin A₁, the enantiomer of the natural product.     

Stereoselective synthesis of (25S)-25-hydroxyvitamin D3 26,23-lactone

Stereoselective synthesis of (25S)-25-hydroxyvitamin D₃ 26,23-lactone ($\text{1w}$) is described starting from C-22 steroidal aldehyde and (S)-citramalic acid. The spectral properties of the compound are almost identical with those of the natural product.     

Novel (4 + 1) fragment combination approach to chiral cyclopentanoids from tartaric acid

A $\text{chiral}$ cyclopentanoid building block $\text{29}$ has been synthesized in “one pot” cyclization process from epoxides $\text{22}$ - $\text{25}$ (which are readily accessible from (R,R)-(+) tartaric acid) with the carbanion derived from phenylthioacetonitrile (PhS-CH₂-CN).     

(2S,5S)-2,5-dibenzyl-1,4-dimethylpiperazine, a novel alkaloid from zanthoxylum arborescens

The isolation and structure determination of (2S,5S)-2,5-dibenzyl-1,4-dimethylpiperazine ($\text{1}$), a new alkaloid biogenetically related to L-phenylalanine diketopiperazine, is described.     

Pathways for migration and cleavage of the S-peptide unit of the leukotrienes

Sulfoxides of leukotriene C ($\text{2}$) and various analogs ($\text{5}$, $\text{8}$) undergo a 1,7-migration of sulfur (forming diastereomers $\text{3}$, $\text{6}$, and $\text{9}$, respectively) with noteworthy facility. Generation of the S-halo derivatives of leukotriene C in water results in heterolysis of the CS bond to give (5S, 12R)- and (5S, 12S)-6-$\text{trans}$-leukotriene B in a process which mimics biochemical deactivation.     

Regioselective intramolecular asymmetric cyclization of symmetrical open chain triketone

The title reactions performed with (S)-α-amino acids or their derivatives as chiral sources were found to regioselectively give enantiomeric pairs of optically active 4-acetyl-3, 4-dimethyl-2-cyclohexenone (R)(+)- and (S)(?)-$\text{4}$), 16–25% e.e., and those of optically active 6-acetyl-3,6-dimethyl-2-cyclohexenone((R)(+)- and (S)(?)-$\text{5}$, 54–59% e.e., from the open chain triketone($\text{3}$).     

New prostaglandin (PGF) derivatives from the soft coral Lobophyton depressum

Four PGF derivatives (15S)-PGF_2α-11-acetate methyl ester ($\text{1}$a), the 18-acetoxy derivative of compound $\text{1}$a ($\text{2}$a) as well as their two corresponding free carboxylic acids ($\text{1}$b) & $\text{2}$b) were isolated from a soft-coral and their structure elucidated, mainly on basis of their spectral data.     

The octant rule. XVI1. COnformation and circular dichroism of syn and anti 2-methylbicyclo[3.1.0]hexan-3-ones,thujone and isothujone

(lS,5S)-exo-2(R)-Methylbicyclo[3.1.0]hexan-3-one ($\text{1}$) and (lS,5S)-endo-2(S)-methylbicyclo[3.1.0]hexan-3-one (2) were synthesized and their circular dichroism (CD) spectra run. Conformational analysis based on molecular mechanics calculations and Karplus equation analyses of vicinal H¦H NMR coupling constants indicate boat-like sofa conformations for both $\text{1}$ and $\text{2}$, with very little ring distortion from the symmetry of the parent bicyclo[3.1.0]hexan-3-one. The lone dissymmetric ψ-axial and ψ-equatorial methyl groups of $\text{1}$ and $\text{2}$, respectively, are both octant consignate. The natural product analogs of $\text{1}$ and $\text{2}$, (?)-3-isothujone ($\text{3}$) and (+)-3-thujone ($\text{4}$) were prepared and examined similarly. Their α-methyl perturbers dominate the CD n-π^★ Cotton effects.     

(S)-citramalic acid,a useful chiral synthon for the synthesis of 15-deoxy-16(S)-hydroxy-16-methylprostaglandins

(S)-Citramalic acid, a readily available microbial metabolite has been efficiently transformed into (2S)-2-methyl-2-hydroxy-1-hexanol ($\text{7}$), an important chiral synthon for the synthesis of 15-deoxy-16(S)-hydroxy-16-methylprostaglandins.