A general approach to γ-lactones via osmium-catalyzed asymmetric dihydroxylation. Synthesis of (−)- and (+)-muricatacin

Dancing Silanols: Stereospecific Rearrangements of Silanol Epoxides into Silanoxy-Tetrahydrofurans and Silanoxy-Tetrahydropyrans

We have developed highly stereospecific rearrangements of silanol epoxides into 1'-silanoxy-tetrahydrofurans and 1'-silanoxy-tetrahydropyrans. Upon treatment with Ph3CBF4 and NaHCO3 in CH2Cl2, di-substituted trans-epoxide silanols rearrange into products with an erythro configuration; di-substituted cis-epoxide silanols give products with a threo configuration. We have used these reactions as key steps in the syntheses of (±)-solerone and (±)-muricatacin.

Study of the β-oxygen effect in the Barton–McCombie reaction for the total synthesis of (4R,5R)-4-hydroxy-γ-decalactone (Japanese orange fly lactone): a carbohydrate based approach

Efficient and facile synthesis of Japanese orange fly lactone (1) was achieved from a commercially available d-glucose by investigating the Barton–McCombie reaction with furanose anomeric isomers (12α, β) with an overall yield of 12.6%. During the course of this synthesis, the β-oxygen effect was discovered in the deoxygenation step at the C-3 position using the Barton–McCombie reaction, where the substrate allows the effect to operate in one of the isomers but not in the other. Under the same reaction conditions, xanthate derived from the β-furanose isomer affords a high yield of deoxygenated product, whereas the α-isomer produces a very low yield. The key transformations used were Wittig olefination, TEMPO mediated oxidation, and Barton–McCombie deoxygenation, resulting in a concise total synthesis of Japanese orange fly lactone (1). Our success will allow for further biological studies of this natural product, as well as opportunities for developing new potentially promising pheromones.

The Japanese orange fly lactone was synthesised with a chiral pool approach using commercially available, starting material d-glucose. This synthesis encountered a dominant structurally functioning impact in the Barton–McCombie reaction known as the β-oxygen effect.

Secondary Metabolites with Antimycobacterial Activities from One Actinobacteria: Herbidospora yilanensis

The cultivation of one actinobacteria strain, Herbidospora yilanensis, was isolated from sediment samples collected from Yilan County City in Taiwan, resulting in the isolation of five previously undescribed compounds: herbidosporayilanensins A-E (1-5), and four compounds isolated from nature for the first time: herbidosporayilanensins F-I (6-9). Their structures were elucidated by spectroscopic analyses, including 1D- and 2D-NMR experiments with those of known analogues, and on the basis of HR-EI-MS mass spectrometry, their antimycobacterial activities were also evaluated.

Stereoselective Total Synthesis of the Dimeric Naphthoquinonopyrano-γ-lactone (-)-Crisamicin A: Introducing the Dimerization Site by a Late-Stage Hartwig Borylation

The first stereoselective total synthesis of the dimeric naphthoquinonopyrano-γ-lactone (-)-crisamicin A was realized (13 steps, 5% overall yield). 1,4,5-Trimethoxynaphthalene, reached in five known steps, was brominated at C-3 to install a but-3-enoic ester by an ensuing Heck coupling. An asymmetric Sharpless dihydroxylation followed and gave a β-hydroxy-γ-lactone with >99.9% ee. Its OH substituent and acetaldehyde established the dihydropyran ring in a completely diastereoselective oxa-Pictet-Spengler cyclization. The 2,3-fused anisole moiety allowed the C⁵-H bond under Hartwig's conditions to be borylated. This set the stage for engaging the resulting C⁵-B bond in an oxidative dimerization, which led to a binaphthohydroquinon-5-yl. The latter was advanced to synthetic crisamicin A by a double CAN oxidation (→ a binaphthoquinon-5-yl) and a double demethylation.

Predominant accumulation of a 3-hydroxy-γ-decalactone in the male rectal gland complex of the Japanese orange fly, Bactrocera tsuneonis

The Japanese orange fly, Bactrocera tsuneonis, infests various citrus crops. While male pheromone components accumulated in the rectal glands are well characterized for Bactrocera, but information regarding the chemical factors involved in the life cycles of B. tsuneonis remains scarce. Herein, several volatile chemicals including a γ-decalactone, (3R,4R)-3-hydroxy-4-decanolide [(3R,4R)-HD], were identified as major components, along with acetamide and spiroketals as minor components in the rectal gland complexes of male B. tsuneonis flies. The lactone (3R,4R)-HD was also identified in female rectal gland complexes. The amount of this compound in mature males was significantly higher than those observed in females and immature males. The lactone (3R,4R)-HD was detected in flies fed with sucrose only, indicating that this lactone is not derived from dietary sources during adulthood, but biosynthesized in vivo. The predominant accumulation of (3R,4R)-HD in mature males also suggests a possible role in reproductive behavior.

An efficient synthesis of an optically active (-)-(3R, 4R, 5R)-4-(1-hydroxyl-isopropyl)-3-acetyloxyl-butyrolactone

An optically active β-hydroxyl–γ-butyrolactone was synthesised from nonchiral starting material by employing reductive cleavage reaction, Sharpless asymmetric epoxidation and dihydroxylation as key steps. This strategy can be used to prepare many chiral β-hydroxyl–γ-butyrolactone analogues. The crystal structure of 10 was determined by X-ray crystallographs.

Chiron approach from D-mannitol to access a diastereomer of the reported structure of an acetogenin, an amide alkaloid and a sex pheromone

A short, simple and convenient chiron approach to (3R,4S,5R)-(-)-3,5-dihydroxy-4-decanolide, a hitherto unknown diastereomer of the reported structure of a naturally occurring acetogenin, (+)-polyporolide has been accomplished starting from a commercially available, inexpensive chiral pool molecule D-(+)-mannitol in nine efficient steps. An advanced intermediate synthesized from D-(+)-mannitol in six steps toward this end was further employed successfully to access two different natural products bearing two contiguous stereogenic centers. As a result, first chiron approach to formal total synthesis of an amide alkaloid, (4R,5R,2E)-4,5-dihydroxy-1-(piperidin-1-yl)dec-2-en-1-one and total synthesis of a male sex pheromone in parasitic Hymenoptera, (4R,5R)-(-)-5-hydroxy-4-decanolide have also been achieved.

Radical-mediated synthesis of γ-lactones by copper-catalyzed intermolecular carboesterification of alkenes with α-carbonyl alkyl bromides and H2O

A novel copper-catalyzed intermolecular carboesterification strategy of alkenes with α-carbonyl alkyl bromides is described.

Total synthesis of cananginone C and structural revision of debilisone A

A short, convergent and general strategy for stereoselective total synthesis of biologically active α-substituted γ-hydroxymethyl γ-lactone based natural products cananginone C and debilisone A has been developed. The salient features of this synthesis include Cadiot-Chodkiewicz coupling, Evans allylation, Sharpless asymmetric dihydroxylation and γ-lactonization. The originally proposed structure of debilisone A has been revised.

A new approach to the side chain formation of 24-alkyl-22-hydroxy steroids: application to the preparation of early brassinolide biosynthetic precursors

A new synthetic route to 22S-hydroxy-24R-methyl steroids has been developed and applied for the preparation of cathasterone, (22S)-hydroxycampesterol, and 6-deoxocathasterone, which are precursors in the early stages of the biosynthesis of brassinolide. The construction of the steroid side chain with the correct stereochemistry at C-24 is based on the use of Claisen rearrangement. The introduction of the 22-hydroxyl group has been achieved by epoxidation of the Δ(22)-double bond, nucleophilic opening of the intermediate mesyl epoxide with sodium sulfide, and desulfurization of the formed tetrahydrothiophenes with Raney nickel.

Efficient oxidation of oleanolic acid derivatives using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP): A convenient 2-step procedure towards 12-oxo-28-carboxylic acid derivatives

A new, straightforward and high yielding procedure to convert oleanolic acid derivatives into the corresponding δ-hydroxy-γ-lactones, by using the convenient oxidizing agent magnesium bis(monoperoxyphthalate) hexahydrate (MMPP) in refluxing acetonitrile, is reported. In addition, a two-step procedure for the preparation of oleanolic 12-oxo-28-carboxylic acid derivatives directly from Δ(12)-oleananes, without the need for an intermediary work-up, and keeping the same reaction solvent in both steps, is described as applied to the synthesis of 3,12-dioxoolean-28-oic acid.

Efficient synthesis of cryptophycin-52 and novel para-alkoxymethyl unit A analogues

Cryptophycins are a family of highly cytotoxic, cyclic depsipeptides. They display antitumour activity that is largely maintained for multi-drug-resistant tumour cells. Cryptophycins are composed of four building blocks (units A-D) that correspond to the respective amino and hydroxy acids. A new synthetic route to unit A allows the selective generation of all four stereogenic centres in a short, efficient and reliable synthesis and contributes to an easier and faster synthesis of cryptophycins. The first two stereogenic centres are introduced by a catalytic asymmetric dihydroxylation, whereas the remaining two stereogenic centres are introduced with substrate control of diastereoselectivity. The stereogenic diol function also serves as the epoxide precursor. The approach was used to synthesise the native unit A building block as well as three para-alkoxymethyl analogues from which cryptophycin-52 and three analogous cryptophycins were prepared. Macrocyclisation of the seco-depsipeptides was based on ring-closing metathesis.

Enantioselective epoxidation of nonconjugated cis-olefins by chiral dioxirane

A variety of nonconjugated cis-olefins has been enantioselectively epoxidized with chiral ketones 2, and up to 92% ee has been obtained. The two prochiral faces of an olefin are likely stereodifferentiated by the relative hydrophobicity of the olefin substituents and/or allylic oxygen functionality.

Short and Efficient Synthesis of Cryptophycin Unit A

[reaction: see text] Two short synthetic approaches toward cryptophycin unit A comprise a catalytic asymmetric dihydroxylation as the sole source of chirality, while all further stereogenic centers are introduced under substrate control. The key step of the first route is a vinylogous Mukaiyama aldol addition, which introduces the alpha,beta-unsaturated ester moiety with defined configuration at the delta-carbon atom. Likewise, allylation with allyltributylstannane diastereoselectively gives the homoallylic alcohol that can be converted by a metathesis reaction to a unit A precursor.

Sequencing of Three-Component Olefin Metatheses: Total Synthesis of Either (+)-Gigantecin or (+)-14-Deoxy-9-oxygigantecin

[Structure: see text] An efficient, flexible, and highly convergent strategy for accessing skipped bis-THF containing Annonaceous acetogenins is demonstrated by the synthesis of each of (+)-gigantecin (1) and its constitutional isomer (+)-14-deoxy-9-oxygigantecin (11). The skeleton of each compound is produced, at will, from the same precursors via a three-component ring-closing/cross-metathesis sequence that differs only in the ordering of the RCM vs CM events. Another notable aspect is the use of in situ epoxide-closing and -opening of iodohydrins with dimethylsulfonium methylide to provide inverted allylic alcohols.

Synthesis of (--)-Muricatacin via alpha- and alpha'-C-H bond functionalization of tetrahydrofuran

(--)-Muricatacin, a potent cytotoxic (4R,5R)-5-hydroxyheptadecan-4-olide, has been synthesized through alpha-C--H hydroxyalkylation and alpha'-C--H oxidation of tetrahydrofuran. This study presents a novel method for C--H bond functionalization as a means for preparing gamma-(hydroxyalkyl)-gamma-butyrolactones.

A formal synthesis of (+)-muricatacin from D-xylose

A multistep route towards the aldehydo-lactone 19, the final chiral precursor in a new stereospecific synthesis of (+)-muricatacin, has been developed starting from D-xylose. The key step of the synthesis involves an E-selective Wittig olefination of the lactol 6 with methoxycarbonylmethylidene triphenylphosphorane, followed by successive catalytic reduction and ?-lactonisation processes. Subsequent selective functional groups interconver- sions furnished the key six-carbon intermediate 19, which can be converted into the (+)-muricatacin via a three-step sequence already described in the chemical literature.