Total synthesis of dolabelide D

The first total synthesis of dolabelide D (or of any of the closely related dolabelides) has been achieved with a longest linear sequence of 17 steps. Key features of the synthesis include an application of the catalytic asymmetric silane alcoholysis, the tandem silylformylation-crotylsilylation, and a Brook-like 1,4-carbon to oxygen silyl migration.     

Total synthesis of pawhuskin C: a directed ortho metalation approach

The total synthesis of the opioid modulator pawhuskin C has been accomplished in eight steps from methyl 3,5-dihydroxybenzoate. The key step in this sequence is a directed ortho metalation reaction conducted without protection of a benzylic alcohol and thus presumed to involve a formal dianion intermediate.     

Total synthesis of kendomycin: a macro-C-glycosidation approach

Kendomycin, also known as (-)-TAN 2162, is a novel polyketide-derived ansamycin isolated from Streptomyces sp., which exhibits potent antagonist and agonist activities at the endothelin and calcitonin receptors, respectively. This bacterial metabolite also possesses a strong antibiotic activity against a range of gram-positive and -negative bacteria and cytostatic effects on the growth of human cancer cell lines. When a novel macroglycosidation reaction is employed as the key step, the first enantioselective total synthesis of kendomycin has been accomplished. A Friedel-Crafts-type ring closure of the acyclic precursor containing tetrahydropyran and benzofuran moieties produces the macrocycle as a single stereoisomer in good yield, thus establishing the aryl C-glycosidic linkage of the ansa core. This reaction requires a phenolic glycosyl acceptor and appears to proceed through a rapid O-glycosidation followed by a slow rearrangement to an aryl C-glycoside. The requisite secomacrocycle is prepared by the Pd(0)-catalyzed B-alkyl Suzuki-Miyaura cross-coupling of two subunits, which in turn can be expeditiously assembled from readily available building blocks in a modular fashion.     

Highly demanding cross-metathesis in the synthesis of the C16-C30 fragment of dolabelide C

A highly demanding cross-metathesis (CM) reaction for the formation of the C24-C25 trisubstituted olefin of dolabelide C has been optimized. A difference in reactivity between the E and Z enone isomers in this reaction was uncovered, and the selection of the Z isomer of the starting enone was critical for the success of the cross-metathesis. Application to the synthesis of the C16-C30 fragment of dolabelide C is reported.     

Total synthesis of aspinolide B: a ring-closing metathesis approach

A highly convergent stereoselective total synthesis of aspinolide B, a 10-membered lactone is described. The key step includes a ring-closing metathesis reaction to construct the 10-membered ring and the E—olefinic moiety. d-Mannitol was used as a chiral pool material for the construction of the key fragments—the olefinic acid and the olefinic alcohol moieties.     

Stereoselective synthesis of the C(1)-C(13) segment of dolabelide B

The efficient construction of the C₁-C₁₃ segment of dolabelide B is described. A key element of the synthesis entails BITIP catalyzed asymmetric methallylation to establish the C₇ stereocenter, which was then used to direct the stereoselective installation of the C₉ and C₁₁ centers through Evans reduction and 1,5-anti aldol condensation, respectively.     

Total synthesis of (+)-discodermolide: a highly convergent fourth-generation approach

[structure: see text] A highly convergent, fourth-generation total synthesis of (+)-discodermolide (1), with a longest linear sequence of 17 steps and an overall yield of 9.0%, has been achieved. Highlighting the strategy is the efficient construction and sequential, bidirectional union of a linchpin comprising the C(9)-C(14) Wittig salt-vinyl iodide (-)-18. Importantly, Wittig salt generation proceeded in excellent yield under ambient pressure.     

Total synthesis of thienamycin: a new approach from aspartic acid

A practical stereospecific synthesis of thienamycin $\text{1}$ has been achieved. Key steps include a lead tetracetate oxidative decarboxylation and subsequent insertion of a four carbon diazo containing unit into a 3-acetoxy-2-azetidinene.     

Total synthesis of branimycin: an evolutionary approach

The first total synthesis of the macrolactone antibiotic branimycin (4) has been described. The key disconnection leads to a cis-dehydrodecalone core and a polyketide side chain which are connected via organometallic addition. The dehydrodecalone core was targeted via altogether five different approaches featuring various kinds of chiral elements and ring-closing methodology. In the end the most successful method starting from diepoxynaphthalene 109 was chosen to carry on with the synthesis. Thus the oxygen functions and carbon appendages were introduced via organometallic desymmetrization reactions to generate epoxy ketone 107, to which vinyl iodide 11 was added after conversion into the organolithium species. The synthesis was completed by introducing the ester side chain via Michael addition and subsequent macrolactonization.     

Total synthesis of aspercyclide C

The first total synthesis of (+)-aspercyclide C (1) is reported using a kinetically controlled RCM reaction to form the 11-membered, unsaturated lactone ring of this bioactive diaryl ether macrolide.     

Total synthesis of isoroquefortine C

A short and efficient total synthesis of isoroquefortine C, the 3,12-(Z)-isomer of roquefortine C, from L-tryptophan methyl ester hydrochloride and 4(5)-(hydroxy)methylimidazole hydrochloride is described.     

Total synthesis of greensporone C

The first total synthesis of greensporone C, a cytotoxic 14-membered resorcylic acid lactone, has been accomplished via a longest linear sequence of 16 steps in 3.3% overall yield. The key features of the synthesis include Mitsunobu esterification and ring-closing metathesis to construct the macrocycle and establish the (E)-olefin geometry, respectively. Our synthesis also confirmed the absolute stereochemistry of the natural product.     

Total synthesis of halichondrin C

The first total synthesis of halichondrin C has been completed, highlighted by development of the synthetic method to construct the C8-C14 polycycle. Cr-mediated coupling reactions are used seven times to form a new C-C bond. The acid stability of halichondrin C is studied, demonstrating that the macrolactone stabilizes the C8-C14 polycycle, relative to the one present in the C1-C16 model.     

Total synthesis of hoiamide C

Hoiamide C was synthesized in 16 steps with an overall yield of 1.8% starting from homoallylic alcohol 18, unambiguously confirming its structure.     

Total synthesis of cyclomarin C

The total synthesis of cyclomarin C was accomplished through a convergent strategy from a tetrapeptide fragment and a tripeptide one. The developed methods to prepare the needed noncoded amino acids, the proper protection of peptide fragments, and identification of the optimum macrocylization site can be applied to further synthetic studies on other members of cyclomarins. [structure: see text]     

Total synthesis of mallotophilippen C

The first total synthesis of mallotophilippen C (1), a bioactive chalcone natural product recently isolated from Mallotus philippinensis MUELL. ARG., is described. The synthesis has been accomplished in 11 linear steps from a commercially available material, with an overall yield of 28%.     

Total synthesis of cryptophycin analogues via a scaffold approach

[reaction: see text] Allylation of in situ generated beta,gamma-unsaturated aldehydes affords rapid access to vinyl halide analogues of fragment A of the cryptophycins. Three scaffolds are prepared in gram quantities by a ring-closing metathesis approach. Derivatization via a variety of cross-coupling protocols is possible, which affords novel analogues of these potent antimitotic agents.     

Ruthenium-SYNPHOS-catalyzed asymmetric hydrogenations: an entry to highly stereoselective synthesis of the C15-C30 subunit of dolabelide A

An efficient construction of the C15-C30 segment of the cytotoxic macrolide dolabelide A is described. The synthesis relies on ruthenium-SYNPHOS-mediated asymmetric hydrogenation reactions of beta-keto esters to generate the C19, C21, and C27 hydroxyl-bearing stereocenters with very high levels of enantio- and diastereoselectivity.