Stereoselective Total Synthesis of Xestodecalactone C

A simple and highly efficient stereoselective total synthesis of xestodecalactone C ( IIb ), a polyketide natural product, was achieved (Scheme 2). The synthesis involved Keck's asymmetric allylation, a iodine‐induced electrophilic cyclization, and an intramolecular Friedel–Crafts acylation as key steps.     

Enantioselective total synthesis of a natural hydrocarbazolone alkaloid,identification of its stereochemistry,and revision of its spectroscopic data

The natural hydrocarbazolone alkaloid (1R,2R,3R)-3-hydroxy-1,2-dimethyl-1,2,3,9-tetrahydro-4H-carbazol-4-one has been synthesized in a catalytic and enantioselective manner. A key hydrocarbazole derivative was constructed by the holmium-catalyzed Diels-Alder reaction of (silyloxyvinyl)indole as the diene. Total synthesis of the natural product clarified the ambiguity in the spectroscopic data reported for natural products.     

Isolation,structural assignment and insecticidal activity of (−)-(1S,2R,3R,4S)-1,2-epoxy-1-methyl-4-(1-methylethyl)-cyclohex-3-yl acetate,a natural product from Minthostachys tomentosa

(−)-(1S,2R,3R,4S)-1,2-Epoxy-1-methyl-4-(1-methylethyl)-cyclohex-3-yl acetate has previously been identified as the active compound of Minthostachys tomentosa responsible for the insecticidal activity against Oncopeltus fasciatus. Its structure was initially assigned on the basis of spectral data. In order to confirm the structure and to define the stereochemistry, stereoselective synthesis of its enantiomer, (+)-(1R,2S,3S,4R)-1,2-epoxy-1-methyl-4-(1-methylethyl)-cyclohex-3-yl acetate, starting from (R)-(−)-piperitone, was carried out using a Sharpless reaction as the key step. The natural product is dextro-rotatory while the synthetic product is levo-rotatory. Measurements of insecticidal activities of the different steroisomers revealed that only the natural product is active.     

Total synthesis of diaportheone A

Diaportheone A (1), a chromone natural product was previously isolated from the endophytic fungi Diaporthe sp. P 133. Its structure was established by spectroscopic methods, however, its absolute configuration remained undefined. This study dealt on the total synthesis of diaportheone A (1) utilizing the cyclization and in situ thermal syn-elimination of a β-ketosulfoxide. The C-1R absolute configuration of the natural product was established by X-ray crystallography of the synthetic diaportheone A (1) (>99%?ee) and comparison with the optical rotation.     

Synthesis of a lactone natural product found in Greek tobacco

A short and stereoselective synthesis of (3R^∗,4R^∗,7R^∗)-3,7-epoxy-4,8-dimethyl-8-nonen-4-olide, a natural product isolated from cured tobacco leaves, has been completed in six steps and 22% overall yield. A samarium(II) iodide mediated reductive cyclisation has been used to construct the functionalised tetrahydropyranol core and subsequent sequential stereoselective addition of methyllithium and lactonisation furnished the natural product.     

Efficient total synthesis of manzacidin B

The highly diastereoselective synthesis of the marine natural product, (?)-manzacidin B, is described. A novel copper-catalyzed aldol reaction of the α-methylserine-derived aldehyde with an isocyanoacetate possessing (1R)-camphorsultam as the chiral auxiliary proceeded in a highly diastereoselective manner to give the (4R,5R,6R)-adduct, which was converted into manzacidin B in a few steps.     

Determination of the absolute configuration of marine oxylipin topsentolide A1 by the synthesis of the enantiomer of the natural product

Two possible stereoisomers of topsentolide A₁, a cytotoxic oxylipin against human solid tumor cell lines, were prepared in order to determine the stereochemistry of natural product. That is, the enantiomer of topsentolide A₁, (8S,11S,12R)-isomer, and its diastereomer was efficiently synthesized in a stereoselective manner. The stereochemistry of topsentolide A₁ was determined to be 8R,11R,12S by comparing NMR spectra and specific rotations of the synthetic isomers and the natural product.     

Isolation and total synthesis of gymnastatin N, a POLO-like kinase 1 active constituent from the fungus Arachniotus punctatus

A high throughput screen against POLO-like kinase 1 (Plk1), an anti-cancer target, identified an active extract from the fungus Arachniotus punctatus. Bioassay guided fractionation led to the isolation of the new natural product, gymnastatin N (1) and the known compound aranorosinol A (2) with IC₅₀ values of 13 and 118 μM, respectively. A 12′-hydroxy analog of gymnastatin N, 3, was also isolated as a minor component. Gymnastatin N (1) was found to be a 52:48 mixture of (1S,6′R) and (1R,6′R) diastereomers, by synthesis of the four possible diastereomers and comparison of the optical rotation and chiral HPLC profile of each diastereoisomer with the natural product. Analogues of 1 were synthesized and evaluated against the Plk1 assay and these SAR studies suggested that the diene and free carboxylic acid moieties might be responsible for its bioactivity.     

Configurational analysis of the natural product passifloricin A by quantum mechanical C NMR GIAO chemical shift calculations

Quantum chemical calculations at mPW1PW91 level, with full geometry optimization, using the 6-31g(d) basis set, and GIAO (gauge including atomic orbitals) ¹³C NMR chemical shifts using the 6-31g(d,p) basis set, are here utilized as a support to define the configurational features of the natural product passifloricin A, whose previously proposed relative configuration has been recently shown, by synthetic studies, to be incorrect. This study suggests that the relative stereostructure for passifloricin A corresponds to the δ-lactone of the (5R,7R,9S,11R)-tetrahydroxyhexacos-2-enoic acid.     

Establishment of the absolute configuration of the bioactive marine alkaloid eudistomin X by stereospecific synthesis

A stereospecific synthesis of both enantiomers of the marine alkaloid eudistomin X using the amino acid chiral pool is achieved. Comparison of ¹H and ¹³C NMR chemical shifts of the synthetic product as either the free base, mono-salt or disalt with those reported for the natural product established that the ascidian metabolite was originally characterised as a mono-salt and that the absolute configuration was (10R).     

Syntheses of the four stereoisomers of Phytophthora mating hormone α2 and a concise synthesis of mating hormone α1

Four stereoisomers of Phytophthora mating hormone α2 were synthesized using both enantiomers of citronellol as starting materials. The absolute configuration of the natural product was determined to be 7S,11R,15R by oospore-inducing assays of the synthetic isomers. A concise synthetic procedure of α1 was also established using a common synthetic intermediate of α2.     

Catalytic asymmetric hetero-Diels–Alder route to a key intermediate for the synthesis of calyxin L

A catalytic asymmetric formal synthesis of diarylheptanoid natural product calyxin L has been achieved by incorporating an enantio- and diastereoselective hetero-Diels–Alder (HDA) reaction, a Suzuki–Miyaura coupling, and a stereocontrolled catalytic hydrogenation of 2,4,6-trisubstituted dihydropyran as the key steps. The HDA reaction between 4-(4-benzyloxyphenyl)-2-triethylsilyloxy-1,3-butadiene and (4-benzenesulfonyloxyphenyl)propynal catalyzed by dirhodium(II) tetrakis[(R)-3-(benzene-fused-phthalimido)-2-piperidinonate], Rh₂(R-BPTPI)₄, provided cis-2,6-disubstituted tetrahydropyran-4-one in 91% yield with 91% ee.     

Challenges in the assignment of relative and absolute configurations of complex molecules: computation can resolve conflicts between theory and experiment

The configuration of (−)-brevianamides was assigned as (2S,13S) based on X-ray structure analysis and hydrolysis experiments. However, our theoretical investigation of its chiroptical properties strongly implied that the correct configuration should be (2R,13R). The reasons for the incorrect earlier assignment are analyzed by calculations of conversion energy barriers among different intermediates, starting materials and final products. This study demonstrates that conflicting theoretical and, experimental results suggest that it is premature to assign the configuration of a natural product.     

Synthesis and stereochemical determination of an antifeeding bisabolanoid from Japanese cedar

The first enantioselective synthesis of (1S,3R,6R)-1-hydroxy-7(14),10-bisaboladien-4-one, a potent antifeedant isolated from the Japanese cedar, Cryptomeria japonica, was achieved starting from methyl (R)-4-hydroxy-3-methylbutanoate via a stereoselective carbonyl ene cyclization reaction as the key step. Comparison of the spectral data and specific rotation of the synthetic material with those of the natural product led to unambiguous stereochemical assignment of the antifeedant as 1S, 3R, and 6R.     

First total synthesis of (+)-Vedelianin, a potent antiproliferative agent

The total synthesis of (+)-vedelianin has been accomplished in 18 steps from vanillin. Preparation of a key intermediate in nonracemic form through a Shi epoxidation has allowed determination of the absolute stereochemistry of the natural product as the (2S,3R,4aR,9aR)-isomer.     

First total syntheses and configurational assignments of cytotoxic trichodenones A–C

Total syntheses of cytotoxic trichodenones A–C, produced by a strain of Trichoderma harzianum from the sponge Halichondria okadai, have been achieved, and the natural trichodenones B and C have been established to have (4R,1′R)- and (1′R)-configurations, respectively. From this synthesis and chiral HPLC analysis, it was deduced that the major molecule with R-configuration coexists with its enantiomer in natural trichodenone A.     

Concise asymmetric synthesis of (R)-(+)-tanikolide

A highly stereoselective total synthesis of (R)-(+)-tanikolide, a δ-lactonic marine natural product, was accomplished in seven steps from easily available starting materials with a 51% overall yield. An asymmetric synthesis of an α-hydroxy aldehyde having a stereogenic quaternary center, by the use of (S)-2-(anilinomethyl)pyrrolidine as a chiral auxiliary, was employed in a key step.     

Synthesis of novel antifungal phthalides produced by a wheat rhizosphere fungus

Two antifungal phthalides produced by a wheat rhizosphere fungus have been synthesized using the Alder-Rickert reaction to construct their common isobenzofuranone core structure. The absolute configuration of one of the two phthalides has been determined to be S by synthesizing its (S)- and (R)-enantiomer and comparing their optical rotations with that of the natural product.     

Enantioselective total synthesis of (2R,3R,6R)-N-methyl-6-(deca-1′,3′,5′-trienyl)-3-methoxy-2-methylpiperidine, an insecticidal alkaloid

An insecticidal piperidine alkaloid, (2R,3R,6R)-N-methyl-6-(deca-1′,3′,5′-trienyl)-3-methoxy-2-methylpiperidine, was efficiently synthesized in a stereoselective manner starting from d-alanine. Chiral center at C-6 was controlled by hydrogenation of imine and side chain was introduced by Julia olefination. The absolute configuration of natural product was determined to be 2R, 3R, 6R.     

An enantioselective total synthesis of the stilbenolignan (−)-aiphanol and the determination of its absolute stereochemistry

The title natural product (−)-aiphanol has been prepared by total synthesis. A key step involved the asymmetric dihydroxylation of (E)-3,5-dimethoxy-4-(methoxymethoxy)cinnamyl alcohol with the AD-mix-β to give triol (1R,2R)-1-(3′,5′-dimethoxy-4′-methoxymethoxyphenyl)-2,3-dihydroxypropanol, the absolute stereochemistry of which was confirmed by single-crystal X-ray analysis of a readily available bromo-derivative. These studies have established that the naturally occurring enantiomer of aiphanol possesses the (S)-configuration at each of C-2′ and C-3′.