The first total synthesis of heteromine B, and an improved synthesis of heteromine A; natural products with antitumor activities

Efficient total syntheses of heteromines A and B (antitumor compounds previously isolated from the plant Heterostemma brownii Hayata) from commercially available 2-amino-6-chloropurine have been developed. The synthesis of heteromine A is considerably shorter than the previously reported synthesis, only requiring four steps, whereas the iodide salt of heteromine B was prepared in five steps. Heteromines A and B showed no significant antibacterial activity and therefore appear to be selective toward cancer cell lines.     

Synthesis of cyclitols via ring-closing metathesis

A convenient synthesis of enantiomerically pure and differentially protected l-chiro- and myo-inositols as well as conduritols B and F from 2,3,4-tri-O-benzyl-d-xylopyranose via ring-closing metathesis is reported. The facile synthesis of conduritol B constitutes a short formal synthesis of (−)-cyclophellitol.     

Total synthesis of maremycins A,B, C1/C2, D1, and D2

The total synthesis of maremycins A, B, C₁/C₂, D₁, and D₂ is achieved starting from the natural amino acids l-isoleucine and S-methyl-l-cysteine, in which the total synthesis of maremycins B, C₁/C₂, and D₂ is accomplished for the first time. The synthesis features a position-selective intramolecular bromination process for the synthesis of key chiral building block, a Pd-catalyzed indole synthesis for the preparation of (2S,3S)-β-methyltryptophan and hydroxylation of oxindoles by molecular oxygen. In addition, the protocol for conversion of maremycins A and B to maremycins C and D was improved.     

Formal total synthesis of aspergillides A and B

The formal total synthesis of the cytotoxic 14-membered macrolides, aspergillides A and B is described. A combination of a chiron approach and an asymmetric synthesis is adopted for the synthesis of the target macrolides. The required 2,6-syn and 2,6-anti tetrahydropyrans were constructed via a tandem Sharpless asymmetric epoxidation and 6-exo cyclization on δ-hydroxy allylic alcohols, as the key steps. The requisite chiral synthon was prepared from l-ascorbic acid.     

Total synthesis of (±) maculalactone A, maculalactone B and maculalactone C and the determination of the absolute configuration of natural (+) maculalactone A by asymmetric synthesis

Maculalactones A, B and C from the marine cyanobacterium Kyrtuthrix maculans are amongst the only compounds based on the tribenzylbutyrolactone skeleton known in nature and (+) maculalactone A from the natural source possesses significant biological activity against various marine herbivores and marine settlers. We now report a concise synthesis of racemic maculalactone A in five steps from inexpensive starting materials. Maculalactones B and C were synthesized by a minor modification to this procedure, and the synthetic design also permitted an asymmetric synthesis of maculalactone A to be achieved in around 85% ee. The (+) and (−) enantiomers of maculalactone A were assigned, respectively, to the S and R configurations on the basis of the chiral selectivity expected for catecholborane reduction of an unsymmetrical ketone in the presence of Corey's oxazoborolidine catalyst. Surprisingly, it appeared that natural (+) maculalactone A was biosynthesized in K. maculans in a partially racemic form, comprising ca. 90-95% of the (S) enantiomer and 5-10% of its (R) enantiomer. Coincidentally therefore, the percentage enantiomeric excess of the product obtained from asymmetric synthesis almost exactly matched that found in nature.     

Enantioselective total syntheses of (+)- and (−)-ottelione A and (+)- and (−)-ottelione B. Absolute configuration of the novel, biologically active natural products

Following our recent total synthesis of the biologically potent natural products otteliones A and B in racemic form, we have now accomplished the total synthesis of both the enantiomers of otteliones A and B through an enantiodivergent strategy emanating from the readily available Diels-Alder adduct of cyclopentadiene and p-benzoquinone. These endeavors have led to the elucidation of the absolute configuration of naturally occurring otteliones A and B.     

A concise total synthesis of arizonins B1 and C1

A concise and efficient total synthesis of arizonins B1 and C1 is reported. A key building block alkyne is synthesized from d-glucono-δ-lactone and used in the Dötz benzannulation reaction to construct the naphthalene unit. An oxa-Pictet–Spengler reaction gave the pyran ring while an H₂SO₄ mediated isomerization set the correct stereochemistry of the target molecules. Alternatively, a direct anti-pyran stereochemistry was prepared in a TFA solvent. The synthesis is competitive to previous reports and marks the first enantioselective synthesis of arizonin B1.     

Chemical and enzymatic synthesis of buprestin A and B—bitter acylglucosides from Australian jewel beetles (Coleoptera: Buprestidae)

A chemical and enzymatic synthesis was developed for buprestin A and B originally isolated from Australian jewel beetles (Coleoptera: Buprestidae). The common motif of both acylglucosides is a β-d-glucopyranose-1,2-bis(pyrrole-2-carboxylate). Starting from 1,3,4,6-tetra-O-acetyl-α-d-glucose, the first pyrrole-2-carboxylate was introduced by DCC-DMAP mediated esterification. After conversion to a trichloroacetimidate the anomeric pyrrole-2-carboxylate was installed. Selective removal of the acetates was accomplished using immobilized Candida antarctica lipase. The resulting triol was converted to Buprestin A or B via a Mitsunobu reaction.     

A straight forward and first total synthesis of Penilumamides B–D

A simple and straight forward first total synthesis of rare lumazine peptides, Penilumamide B, C and D isolated from the marine-derived fungi Aspergillus and Penicillium sp. is described from a common starting material, 1,3-dimethyllumazine-6-carboxylic acid. Penilumamide C was prepared from Penilumamide B by oxidation of the methionine residue to the corresponding sulphone.     

The stereoselective total syntheses of pectinolides A,B, and C

The stereoselective total synthesis of pectinolide B has been accomplished for the first time along with total syntheses of pectinolides A and C. MacMillan α-hydroxylation and Sharpless asymmetric dihydroxylation reactions are involved in generating the three stereogenic centers. Other important transformations in the synthesis are Z-selective Still–Gennari olefination, selective benzylation of the homoallylic alcohol, and a one-pot MOM deprotection followed by lactonization leading to all three pectinolides A–C being synthesized from a common intermediate. Pectinolides A, B, and C were synthesized from n-hexanal in 19, 20, and 18 steps with overall yields of 8.8%, 6.72%, and 9.2%, respectively.     

First total synthesis of glabramycin B and revision of its relative configuration

Structural revision of glabramycin B, which is an antibacterial 10-membered lactone isolated from a fermentation broth of Neosartorya glabra, was achieved by enantioselective synthesis of our proposed structure. The correct structure of glabramycin B was presumed on comparison with related compounds, and synthesis of it was succeeded via dianion alkylation, Shiina's lactonization and Stille cross-coupling. By this synthesis, we were able to correct the reported structural misassignment, and to confirm the relative configuration of glabramycin B to be 10S*,11S*,15R*,20S*.     

Concise total synthesis of phidianidine A and B

The shortest total synthesis of cytotoxic indole alkaloids phidianidine A and B is described. Rapid assembly of the 1,2,4-oxadiazole core from a novel N-hydroxyguanidine and the corresponding indole-3-acetic acid chloride led to formal syntheses of phidianidine A and B in only three steps from known compounds. Deprotection under standard conditions provided the trifluoroacetate salts of phidianidine A and B in quantitative yield.     

An enantioselective synthesis of a MEM-protected aetheramide A derivative

Aetheramides A and B are very potent anti-HIV agents. An enantioselective synthesis of a MEM-protected aetheramide A derivative is described. The synthesis was accomplished in a convergent and stereoselective manner. The key reactions involved asymmetric dihydroxylation, asymmetric allylation, asymmetric syn-aldol reactions, and asymmetric hydrogenation.     

Synthesis of streptorubin B core

A straightforward synthesis of streptorubin B core structure has been established starting from trans-4-hydroxyproline. The core structure of streptorubin B is constructed in an intramolecular ring-closing metathesis as the key step.     

Enantioselective total synthesis of (−)-epoxyquinols A and B. Novel, convenient access to chiral epoxyquinone building blocks through enzymatic desymmetrization

Following our recent total synthesis of the biologically potent natural products epoxyquinols A and B in racemic form, we have now accomplished the total synthesis of the (−)-epoxyquinols A and B, anti-podes of the angiogenesis inhibiting natural products, through a protocol that involves enzymatic desymmetrization of a versatile epoxyquinone derivative, readily available from the Diels-Alder adduct of cyclopentadiene and p-benzoquinone.     

New chiral building blocks from acetovanillone using lipase A and B from Candida antarctica

Acetovanillone has been used as the starting material for the synthesis of a series of secondary alcohols, which were resolved by lipase catalyzed esterification. 1-(4-Benzyloxy-3-methoxyphenyl)ethanol was efficiently resolved using immobilized lipase B from Candida antarctica (Novozym 435, CAL-B), whereas immobilized lipase A from C. antarctica (Novozym 735, CAL-A) was the lipase of choice for the resolution of the corresponding 2-bromo- and 2-chloro-derivatives. The enantioenriched alcohols are new building blocks for potential use in the synthesis of bioactive compounds.     

Total synthesis of emericellamides A and B

A concise total synthesis of emericellamides A and B, two cyclic depsipeptides exhibiting antibacterial and cytotoxic activities, is reported. A Paterson anti-aldol reaction and a hydroxy directed 1,3-anti reduction were applied for construction of the polypropionate unit with the required stereochemistry in emericellamides A and B. An FDPP mediated macrolactamization was used to construct the macrocycle of emericellamides A and B.     

A general route to 5,6-seco-hexahydrodibenzopyrans and analogues: first total synthesis of (+)-Machaeridiol B and (+)-Machaeriol B

A general and efficient route for the synthesis of 5,6-seco-hexahydrodibenzopyran and trans-hexahydrodibenzopyran analogues was established, via a highly regio- and stereoselective S_N2′ reaction of arylcyanocuprates to enol silyl ether of α,β-epoxycyclohexanone. It was applied to the first facile total synthesis of (+)-Machaeridiol B and (+)-Machaeriol B.     

Stereoselective synthesis of pachastrissamine (jaspine B)

A stereoselective synthesis in enantiopure form of the natural anhydrophytosphingosine pachastrissamine (jaspine B), a metabolite isolated from sponges, is described. The chiral epoxide (R)-glycidol was the starting material. Key steps of this synthesis are a Sharpless asymmetric epoxidation, an intramolecular stereospecific epoxide opening mediated by a trichloroacetimidate group, and the formation of a tetrahydrofuran ring via intramolecular nucleophilic displacement.     

Total synthesis of (−)-jaspine B and its 4-epi-analogue from d-xylose

The total synthesis of the HCl salts of (−)-jaspine B ent-1 and its 4-epi-congener ent-4 was accomplished starting from the common template 13 derived from d-xylose. The cornerstone of our synthesis was [3,3]-heterosigmatropic rearrangements, which effectively provided scaffolds with a chiral amino group. A subsequent Wittig olefination installed a C₁₄ alkyl side chain and acid-mediated ring-closing reaction established the tetrahydrofuran core.