CC bond formation from schiff base and vinyloxyborane: Synthesis of β-amino acid derivatives

An efficient methodology for the preparation of β-amino acid derivatives ($\text{3}$) by CC bond formation from Schiff bases ($\text{1}$) and vinyloxyborane ($\text{2}$) and their utilization in the synthesis of the pyrimidine moiety ($\text{3f}$) of bleomycin are described.     

Carbocyclic analogs of C-nucleosides: a key intermediate via a novel and efficient CC ring scission

Treatment of hydroxymethylene ketone $\text{6}$ with trimethylene dithiotosylate according to literature conditions,^3b led to the novel CC ring scission product $\text{7}$ in high yield; also, the hydroxide-initiated cleavage⁴ of $\text{1}$ gave the β-elimination product $\text{13}$ which underwent a highly stereospecific addition of diazomethane to provide $\text{15}$.     

Structure of protoveratrine C,a new alkaloid from provoveratrine

Single-crystal $\text{X}$-ray analysis has established that provoveratrine C, a third tetraester component of proveratrine, is protoverine 3-(2′$\text{S}$,3′$\text{R}$-2′,3′-dihydroxy-2′-methylbutyrate 6,7-diacetate 15-(2′$\text{R}$)-methylbutyrate.     

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.     

Isolation ofΔ9(11)-sterols from the sea cucumber psolusfabricii. Implications for holothurin biosynthesis

- 14α-Methyl-5α-cholest-9(11)-en-3β-ol ($\text{2}$) and 4α,14α-dimethyl-5α-cholest-9(11)-en-3β-ol ($\text{3}$) have been isolated from the sea cucumber $\text{Psolus}$$\text{fabricii}$ and characterised by ¹H NMR, ¹³C NMR and mass spectrometry. Lanost-9(11)-en-3β-ol ($\text{4}$) has also been tentatively identified. The relevance of this series of Δ⁹⁽¹¹⁾-sterols to holothurin biosynthesis is briefly discussed.     

Conformational effects in compounds with 6-membered rings—XIII : Detection of twist conformers using 13C NMR chemical shifts

¹³C NMR spectra of derivatives of cyclohexane, piperidine, and thian in chair and twist eonformers, and of model compounds, lead to estimates of deshielding (Δδ = 3.6 ± 0.2 ppm) for axial C$\text{Me}$₃ on a cyclohexane ring and shielding (Δδ = ?0.2 to ?0.6 ppm) for ψe-C$\text{Me}$₃ in twist conformers, relative to equatorial C$\text{Me}$₃. Ring carbon atoms are considerably shielded in twist conformers relative to chair eonformers. The value of ¹³C chemical shifts in the study of chair-twist equilibria is exemplified by variable temperature measurements on diastereomeric pairs of compounds (11 and 13; 38 and 50).     

Shinjulactone C,a new quassinoid ith a 1α, 12α:5α, 13α-dicyclo-9βH-picrasane skeleton from ailanthus altissima SWINGLE

A new non-bitter quassinoid, named shinjulactone C ($\text{1}$), was isolated from the root bark of $\text{Ailanthus altissima}$ SWINGLE and shown to be 1α, 12α:5α, 13α-dicyclo-1β, 12β, 20-trihydroxy-9β$\text{H}$-picras-3-ene-2, 11, 16-trione by X-ray diffraction method.     

Chiral recognition of alkene and arene hydrocarbons by 1H and 13C NMR. determination of enantiomeric purity

Simultaneous presence of the salt $\text{1}$ and one of the lanthanide complexes (+)-$\text{2}$, (+)-$\text{3}$, or (+)-$\text{4}$ splits ¹H or ¹³C NMR signals of the chiral alkenes $\text{5}$, $\text{6}$, and $\text{8}$ as well as of the chiral arene $\text{7}$; the enantiomeric purity of a mixture of (+)- and (?)-$\text{8}$ was determined successfully.     

Synthetic studies of polyene macrolides,synthesis of a C29–37 fragment for amphotericin B and nystatin

An enantioselective synthesis of a C29–37 fragment common to both amphotericin B $\text{1}$ and nystatin $\text{2}$ is described from ethyl 3(S)-hydroxybutanote.     

The structure of brevetoxin C

The structure of brevetoxin C (BTX-C), a polyether marine toxin from $\text{Ptychodiscus}$$\text{brevis}$, has been elucidated by comparison of its spectral data with those of brevetoxin B (BTX-B).     

Synthesis of (+) dictyopterene a constituent of marine brown algae and (+) dictyopterene C′ by chirality transfer of optically active allylic benzoate with palladium (O) catalyst.

The first enantioselective syntheses of (+) dictyopterene A $\text{1}$ and (+)dictyopterene C′ were reported. The key reaction was based on palladium promoted cyclisation of chiral allylic benzoate $\text{5}$ with transfer of chirality (anti attack of the palladium with respect to the leaving group) to give optically active vinylcyclopropane $\text{7}$ with (R) configuration which contains proper functionality for further elaboration into $\text{1}$ and $\text{3}$     

Total synthesis of slow reacting substances (SRS). “Leukotriene C-2” (11-trans-leukotriene C) (3) and leukotriene D (4)

Syntheses are described for the “slow reacting substances” 11-$\text{trans}$-leukotriene C (3) (previously known as leukotriene C-2) and leukotriene D (4), the cys-gly analog of leukotriene C (2). The synthesized leukotrienes 3 and 4 were instrumental in the assignment of structure to these members of the family of naturally occuring slow reacting substances which includes also 2.     

Total synthesis of slow reacting substances (SRS's): 6-epi-leukotriene C and 6-epi-leukotriene D

6-$\text{Epi}$-leukotrienes C and D (3 and 4) have been synthesized unambiguously via the 5($\text{S}$), 6($\text{R}$)-epoxide (5,6-$\text{cis}$) which is isomeric with leukotriene A. These 6-$\text{epi}$-leukotrienes are less active (especially 4) than leukotrienes C and D (1 and 2) and have not been found in substantial quantity in natural SRS sources.     

The Mannich reaction of 9-acetyl- and 9,10-dihydro-9-acetylanthracene. Reduction of the Mannich bases, and stereochemistry of the 9,10-dihydro compound

The Mannich derivatives ($\text{2}$ and $\text{5}$) of 9-acetyl-9,10-dihydroanthracene ($\text{4}$) with amines of different sizes were prepared for study of their biological effects. It was found that formation of the normal Mannich product in acetic acid was accompanied by formation of a secondary Mannich product containing a methylidene group ($\text{3}$ and $\text{6}$). Reduction of compounds $\text{5}$ with NaBH₄ gave aminoalcohols ($\text{10}$), and amino-olefins ($\text{11}$) were prepared from these by elimination. The catalytic reduction of compounds $\text{2}$ on Pd/C, Raney Ni and Adams catalysts was studied under acidic and basic conditions. In acidic media on Pd/C, the 9,10-dihydro compounds ($\text{5}$) were formed; under basic conditions, on all three catalysts the hydrogenation led to deamination. However, for “steric hindrance” reasons the keto group was not reduced in any of the cases. In compounds $\text{5}$, the literature data and the H-NMR spectra indicate that the orientation of the 9-substituent is pseudoaxial     

Biosynthesis of highly modified meroterpenoids in aspergillus variecolor. Incorporation of 13C-labelled acetates and methionine into anditomin and andilesin C

Incorporations of [1-¹³C]?, [2-¹³C]?, [1,2-¹³C₂]-acetates and [¹³C]-methionine into anditomin, a metabolite of $\text{Aspergillus variecolor}$, indicate its formation by a mixed polyketide-terpenoid biosynthetic pathway similar to that elucidated for andibenin; observations are made on the possible biosynthetic relationship of the $\text{A. variecolor}$ metabolites with austin and terretonin, mycotoxins recently isolated from $\text{A. ustus}$ and $\text{A. terreus}$ respectively.     

Chiral 1,4-benzodiazepines—-XI: Kinetics of degenerate nucleophilic exchange of C(3)-hydroxy group

The rate for degenerate nucleophilic exchange (k_e) of the C(3)-OH group in the racemic compound 1 was determined in DMSO/H₂¹⁸O using mass spectrometry. Epimerization rates for diastereomers 15 and 16 were determined by polarimetry (k_ep) and NMR spectroscopy (k_r-c—for $\text{r}$ing-$\text{c}$hain tautomery). The ratio $\text{k}{}_{\mathrm{e}}\text{k}{}_{\mathrm{ep}}$ ~ 3.5 35° is close to that obtained for degenerate nucleophilic exchange of the C(3)-OMe group in the compound 1a ($\text{k}{}_{\mathrm{e}}\text{k}{}_{\mathrm{\alpha }}$ ~4, Refs. [3,4]). These data confirm the C(3)-OH substituted 1,4-benzodiazepin-2-ones lose the configurational identity of the C(3) chiral centre by both direct nucleophilic substitution of the OH group, and ring-chain tautomery processes.The synthesis of the diastereomeric compounds 15 and 16, and their chromatographic separation is described.     

Synthesis and conformational behaviour of 1,9,17-triaza[2.2.2]metacyclophane-2, 10, 18-trione derivatives

The 1,9,17-triaza[2.2.2]metacyclophane-2, 10, 18-trione derivatives ($\text{1}$) – ($\text{3}$) have been synthesised. X-Ray crystallography shows that the 1,9,17-trimethyl derivative ($\text{3}$) adopts a Crown conformation ($\text{11}$) in the solid state. Dynamic n.m.r. spectroscopy indicates that both the 1,9-dimethyl-17-benzyl- ($\text{2}$) and 1,9,17-trimethyl- ($\text{3}$) derivatives exist as interconverting mixtures of Crown ($\text{11}$) and Saddle ($\text{12}$) conformations with the former predominating at equilibrium in solution.     

Synthetic studies on antibiotic A23187 I. Chiral synthons for C9-C13 and C14-C20

Chiral synthons $\text{3}$ and $\text{4}$ for the synthesis of antibiotic A23187 $\text{1}$ were prepared from methyl α-D-glucopyranoside.