Short diastereoselective synthesis of the C1-C13 (AB spiroacetal) and C17-C28 fragments (CD spiroacetal) of spongistatin 1 and 2 through double chain-elongation reactions

A unique and practical synthetic sequence for rapid access to polyketides and to further the spiroacetals derived from them, which utilizes a bidirectional Hosomi-Sakurai allylation approach around key allylsilanes in the synthesis of the AB and CD ring systems of spongistatin 1 and 2, is reported. The synthesis of the AB spiroacetal 9 requires 13 steps, with a longest linear sequence of seven steps in an overall yield of 27%. The synthesis of the CD spiroacetal 13 requires 15 steps, with a longest linear sequence of 11 steps in an overall yield of 30%. Both syntheses start from but-3-enol.     

Total synthesis of lamellarins D, H, and R and ningalin B

A concise total synthesis of lamellarins D (7 steps), H (7 steps), and R (5 steps) and ningalin B (5 steps) is achieved starting from the corresponding aldehydes and amines. The synthesis features three oxidative reactions as key steps in a biomimetic manner, involving an AgOAc-mediated oxidative coupling reaction to construct the pyrrole core, a Pb(OAc)(4)-induced oxidative cyclization to form the lactone, and Kita's oxidation reaction to form the pyrrole-arene C-C bond.     

Expedient total synthesis of pyrrothine natural products and analogs

This paper describes an expedient and straightforward total synthesis of the two pyrrothine natural products holomycin (7 steps, 11% overall) and xenorhabdin I (7 steps, 11% overall) and analogs thereof via a common late-stage intermediate. The pathway proceeds via the pyrrothine hydrochloride intermediate (6 steps, 17% overall) which also gave access to very fast synthesis of analogs as demonstrated by the synthesis of , and (7 steps, 11-12% overall).     

A short total synthesis of (±)-epimeloscine and (±)-meloscine enabled by a cascade radical annulation of a divinylcyclopropane

The first stereoselective synthesis of epimeloscine has been accomplished in 13 total steps with a longest linear sequence of 10 steps. The core of the synthesis takes only five steps, the key ones being acylation, stereoselective tandem radical cyclization of a divinylcyclopropane to make two rings, and group-selective ring-closing metathesis of the resulting divinylcyclopentane to make the last ring.     

Diverse synthesis of the C ring fragment of bryostatins via Zn/Cu-promoted conjugate addition of α-hydroxy iodide with enone

A convergent approach to 1,5-hydroxy ketones,the general precursors for constructing the C ring of bryostatins,has been developed via a Zn/Cu-promoted conjugate addition of a-hydroxy iodides with enones.The reaction leads to direct formation of the C21-C22 bond and tolerates diverse functionalities at the C17-,C18-and C24-positions.The approach also enables a more concise synthesis of the known C ring intermediate(10 longest linear steps and 14 total steps),in contrast to its previous synthesis(17 longest linear steps and 22 total steps) in our total synthesis of bryostatin 8.     

Synthesis of conformationally constrained lysine analogues

The synthesis of two conformationally constrained lysine analogues is reported. The synthesis of the novel analogue 1 based on the 3-aza-bicyclo[3.1.0]hexane system is accomplished from the known tricycle 3 in eight steps. The synthesis of the analogue 2 is accomplished in eight steps from 4-hydroxy proline. Both analogues are synthesized appropriately protected for Fmoc/Boc solid-phase peptide synthesis.     

A concise and improved synthesis of (+)-eleutherin, (+)-allo-eleutherin and a formal synthesis of (+)-nocardione B

A concise and improved stereoselective synthesis of (+)-eleutherin, (+)-allo-eleutherin and the formal synthesis of (+)-nocardione B is described. The synthesis is based on a Dötz benzannulation and an improved oxa-Pictet-Spengler cyclization as the key steps. The synthesis is achieved in six steps in overall yields of 18% for eleutherin and 20% for allo-eleutherin.     

Synthesis of santiagonamine

The first total synthesis of santiagonamine (1) is achieved in 12 steps from isovanillin. A palladium-catalyzed Ullmann cross-coupling reaction and a photocyclization are the key steps in the synthesis.     

Total synthesis of Carpatamides A–D

A synthetic strategy was developed for the synthesis of the common core structure of Carpatamides A–D. The total synthesis of Carpatamides A and C was completed in 6 steps and of Carpatamides B and D in 7 steps, by employing the Wittig olefination, olefin cross metathesis and acid amine coupling reactions as key steps.     

An approach to the skeleton of the securinega alkaloids. The total synthesis of (+/-)-securinine

[structure: see text]. The concise total synthesis of securinine in nine steps from readily available starting materials is described. Key steps of the synthesis include an addition of a silyloxyfuran to an in situ generated iminium ion and a novel ring closing metathesis reaction.     

Total synthesis of (+)-nakadomarin A

The total synthesis of (+)-nakadomarin A is described. A three-component cycloaddition of a hydroxylamine, aldehyde, and cyclopropane to form a highly functionalized tetrahydro-1,2-oxazine serves as the foundation for this synthesis. The resulting oxazine is formed as a single diastereomer with the absolute configuration being dictated by the chirality of the cyclopropane. Other key steps include: desymmetrization of a malonate by reduction, Heck cyclization and pyrrolidine formation, and ring-closing metathesis to form both cycloalkenes. Overall, the synthesis required 23 linear steps from the cyclopropane, which in turn is available (six steps) in optically pure form from commercially available d-mannitol.     

Unified total synthesis of the natural products endiandric acid A,kingianic acid E,and kingianins A,D, and F

A measure of the strength of a synthetic strategy is its versatility: specifically, whether it allows structurally distinct targets to be prepared. Herein we disclose a unified approach for the total synthesis of natural products of three distinct structural types, all of which occur naturally as racemic mixtures. The point of divergence involves the terminal alkylation of a conjugated tetrayne, and culminates in a significantly shortened synthesis of endiandric acid A (8 steps), the first total synthesis of kingianic acid E (8 steps), and a second-generation synthesis of kingianins A, D, and F (11 steps). Evidence for redox catalysis in the biosynthesis of kingianic acid E is presented.     

Concise enantioselective total synthesis of neopeltolide macrolactone highlighted by ether transfer

A concise total synthesis of neopeltolide macrolactone has been accomplished in 14 steps in the longest linear sequence, 15 steps overall from commercially available materials. The present synthesis was highlighted by successful exploitation of ether transfer methodology and a radical cyclization reaction to directly establish the requisite stereochemistry of the tetrahydropyran core.     

An enantioselective synthesis of tarchonanthuslactone

An enantioselective synthesis of tarchonanthuslactone has been achieved in eight steps from ethyl sorbate. The asymmetry of the route was introduced via a Sharpless asymmetric dihydroxylation allowing access to either enantiomer. The synthesis utilizes a palladium-catalyzed reduction and a diastereoselective base-catalyzed acetal formation as the key steps. The pyran ring of tarchonanthuslactone was established by a Still-olefination/lactonization sequence. DCC-mediated attachment of dihydrocaffeic acid completed the synthesis of tarchonanthuslactone in a 19% overall yield.     

Total synthesis of (-)-13-oxyingenol and its natural derivative

Ring functionalization: the total synthesis of a natural derivative of (-)-13-oxyingenol, a potent anti-HIV diterpenoid, is reported. The key steps in this synthesis include a ring-closing olefin metathesis and a Mislow-Evans-type [2,3]-sigmatropic rearrangement. This synthesis provides access to (-)-13-oxyingenol and its natural derivative in 21 steps from a synthetic intermediate previously prepared by Kigoshi and co-workers.     

Total synthesis of (+)-laurencin: an asymmetric alkylation-ring-closing metathesis approach to medium ring ethers

[formula: see text] The enantioselective total synthesis of (+)-laurencin 1 is achieved in 18 steps from (S)-(+)-4-benzyl-3-benzyloxyacetyl-2-oxazolidinone. The key steps in this synthesis are an asymmetric glycolate alkylation leading to acyl oxazolidinone 2 and a subsequent ring-closing olefin metathesis to construct the oxocene core of 1. The approach to medium ring ethers utilized in this synthesis provides a general and efficient route to the cyclic core of other marine natural products.     

Enantioselective allyltitanations and metathesis reactions. Application to the synthesis of piperidine alkaloids (+)-sedamine and (-)-prosophylline

An enantioselective synthesis of the piperidine alkaloids (+)-sedamine and (-)-prosophylline is reported. The synthesis of (+)-sedamine has been achieved in 12 steps with an overall yield of 20% from benzaldehyde, and (-)-prosophylline was obtained in 15 steps with an overall yield of 9.2%, starting from D-glyceraldehyde acetonide 14. The key steps are enantioselective allyltitanation reactions and ring-closing or cross-metathesis reactions.     

Total synthesis of (+/-)-acetomycin and design of esterase-resistant analogs.

The synthesis of acetomycin and related analogs was investigated. Acetomycin was synthesized from diethyl allyl(methyl)malonate in 6.5% yield over 18 steps. The total number of steps was improved compared to our previous synthesis; i.e., four steps shorter, and the total yield was 4.5% greater than the previous synthesis. Acetomycin analogs with benzoyloxy and pivaloyloxy groups, instead of an acetoxy group at the 5-position of the gamma-butyrolactone ring were designed as esterase-resistant models and prepared similarly. Although they showed a similar level of cytotoxicity as acetomycin in vitro, they were not resistant to porcine liver esterase, and lost cytotoxicity in vivo.     

Furanosteroid studies. Improved synthesis of the A,B,C,E-ring core of viridin

The tetracyclic core skeleton of the furanosteroid viridin is prepared in nine steps from readily available materials. The key step in the synthesis is a facile acid-promoted cyclodehydration of an aryloxyketone to prepare the benzofuran moiety. From this intermediate, the known target skeleton is prepared in four steps. This new synthesis is a six-step improvement over the previously reported one.     

Total synthesis of BE-43547A2

An asymmetric total synthesis of BE-43547A₂ has been achieved in 16 steps (longest linear) on a 3.2 gram scale. The details of our efforts that led to the total synthesis of BE-43547A₂ were reported, the final 6 steps were optimized, and the overall yield was improved from 4.5% to 9.7%. The procedure utilized in the final 2 steps may serve as a better method for separating unstable APD compounds.