Synthesis of (+)-goniopypyrone and (+)-goniotriol using Pd-catalyzed carbonylation

Syntheses of (+)-goniopypyrone and (+)-goniotriol isolated from Goniothalamus giganteus were achieved. The key steps involve Pd-catalyzed carbonylation for lactone ring formation and diastereoselective reduction of ynone using the (R)-CBS catalyst and borane dimethyl sulfide complex.     

Total Synthesis of (+)-Lactacystin

A double stereodifferentiating crotylation between aldehyde 1 and silane (S)- 2 to afford homoallylic alcohol 3 is the key diastereoselective step (anti:syn >30:1) in an efficient asymmetric synthesis of (+)-lactacystin. This compound is a metabolite isolated from Streptomyces sp. OM-6519 that exhibits significant neurotrophic activity. An additional important step in the synthesis is a catalytic asymmetric aminohydroxylation used as the key step in the synthesis of the (2R,3S)-hydroxyleucine synthon.     

Synthesis of a Greek tobacco lactonic natural product and its analogues

A total synthesis of a Greek tobacco lactonic natural product and three of its analogues has been achieved using a commercially available starting material and our furan approach to oxacyclic systems, the proven scope of which is thus broadened.     

Total synthesis of (+)-boronolide, (+)-deacetylboronolide,and (+)-dideacetylboronolide

Total synthesis of (+)-boronolide, (+)-deacetylboronolide, and (+)-dideacetylboronolide has been achieved from a single intermediate 26, which was synthesized in 11 steps from a d-mannitol-derived intermediate 8 in an overall yield of 10%. The key steps in the synthesis are inversion of a chiral center by taking an advantage of the inherent mechanism involved in the ring closing to an epoxide via intramolecular S(N)2 reaction and lactonization of a diol using Fetizons reagent. The strategy is amenable to preparation of analogues of (+)-boronolide in sufficient amount for further screening of biological activity.     

Total Synthesis of (+)-Gelsedine

A novel iodide-promoted, allene-terminated cyclization of an N-acyliminium ion, a stereoselective Heck spirocyclization, and a chemoselective demethylation at the nitrogen atom of an oxindole are the key transformations in the first total synthesis of the indole alkaloid (+)-gelsedine ( 1 ). This dextrorotatory form of natural gelsedine was formed as a single enantiomer in 21 steps from (S)-malic acid.     

Total Synthesis of the Proposed Structure of (+)-Tolyporphin A O,O-Diacetate

Four monocyclic precursors were assembled in the total synthesis of the proposed structure 1 - A of (+)-tolyporphin A O,O-diacetate (X=Ac). Comparison of the spectroscopic data demonstrated that synthetic tolyporphin O,O-diacetate did not match the O,O-diacetate prepared from natural (+)-tolyporphin A (X=H), calling for a structural revision of this class of natural products. On the basis of a series of NMR experiments including synthetic intermediates, the structure of tolyporphin A is concluded to be 1 - B , in which the configurations of quaternary centers C7 and C17 are opposite to those in the originally proposed structure.     

Asymmetric Total Synthesis of Fredericamycin A

Seventeen years after the isolation of the promising antitumor antibiotic fredericamycin A, the first asymmetric total synthesis of this compound has been accomplished and thereby its absolute configuration established. The key feature is the regiocontrolled [4+2] cycloaddition of 3 to 2 , which was obtained by the stereospecific rearrangement of 1 . Cp = (−)‐camphanoyl.     

Stereoselective total synthesis of (+)-boronolide

A seteroselective total synthesis of (+)-boronolide is described. The key steps are Sharpless asymmetric dihydroxylation, Shibasaki's asymmetric Henry reaction, asymmetric allylation and ring closing metathesis.     

Concise and Efficient Total Syntheses of Alkannin and Shikonin

Two enantiomic natural products with wound-healing properties , alkannin ( 1 ) and shikonin ( 2 ), are accessible by a short and efficient total synthesis. The success was achieved by a novel protecting system for masking of 5,8-dihydroxy-1,4-naphthoquinones (naphthazarins) and a highly stereoselective ketone reduction.     

(+)-MethylCembra-1,3,7,11-tetraene-16-carboxynate的不对称合成研究

The first asymmetric synthesis of ( )-methyl cembra-1,3,7,11-tetraene-16-carboxynate, a naturally occurring cembrane-type macrocyclic diterpene isolated from Sinularia mayi, was achieved via general approach by employing an intramolecular McMurry coupling and Sharpless asymmetric epoxidation as the key steps from readily available starting materials. The synthesis presented here verifies that the absolute configuration of compound 1 was assumed as 15R.     

Total Synthesis of Chatancin

As an antagonist of the platelet activating factor , chatancin ( 1 ), which is isolated from a soft coral, is of potential therapeutic use. The first total synthesis [Eq. (1)] of this structurally unusual diterpene in racemic form is described along with the formal total syntheses of natural (+)-chatancin as well as unnatural (−)-chatancin.     

Stereoselective synthesis of (−)-cytoxazone and (+)-epi-cytoxazone

Optically pure (−)-cytoxazone was synthesized, starting from methyl p-methoxycinnamate, in six steps and in 31% overall yield. The required anti-aminoalcohol configuration was established by combining Sharpless asymmetric aminohydroxylation with the configurational inversion of the intermediate amidoalcohol via an oxazoline. The synthesis of (+)-epi-cytoxazone is also described.     

Total Synthesis of Macrolactin A with Versatile Catalytic,Enantioselective Dienolate Aldol Addition Reactions

A highly convergent total synthesis of macrolactin A ( 1 ) utilizes modern asymmetric catalytic C–C coupling methods. The longest linear sequence in the route is 16 steps with an average yield of 86% per step. This total synthesis is valuable, because 1 , which has been shown to possess activity against HIV, is not readily accessible from its natural source, a taxonomically unclassified deep-sea bacterium.     

Stereoselective total synthesis of (+)-boronolide, (+)-anamarine, 8-epi-spicegerolide

A stereoselective total synthesis of the naturally occurring cytotoxic lactones (+)-boronolide, (+)-anamarine, and 8-epi-spicigerolide is described. d-Xylose has been used as a chiral source to construct the four contiguous oxygenated stereogenic centers of target molecules. The diastereoselective allylation was performed using Brown’s protocol and the lactone moiety was prepared by ring closing metathesis.     

Total synthesis of (+)-blennolide C and (+)-gonytolide C via spirochromanone

We report the asymmetric total synthesis of (+)-blennolide C and (+)-gonytolide C isolated from endophytic fungi. The synthesis involved construction of a spirochromanone with a chiral quaternary carbon by the aldol reaction of o-hydroxyacetophenones and optically active α-oxygenated cyclohexenone, followed by cyclization under acidic conditions. Oxidative cleavage of the alkene moiety of the spirochromanone furnished the chromanone diester. Through treating the diester with a Lewis acid, the first total synthesis of (+)-blennolide C was achieved by deprotecting the oxygen functionality of the diester and simultaneous Dieckmann condensation. Total synthesis of (+)-gonytolide C was also achieved by lactone formation from the deprotected diester.     

Stereocontrolled Synthesis of (−)-5,11-Dideoxytetrodotoxin

New derivatives of an intriguing marine natural product are now accessible. The first asymmetric synthesis of the simple tetrodotoxin analogue, 5,11-dideoxytetrodotoxin ( 3 ), was achieved. Hydroxylation at position C8 of the key intermediate 1 relied on the neighboring trichloroacetamide group, and stereoselective elaboration of the vinyl group gave α-hydroxylactone 2 , which was transformed into the title compound through a new guanidylation method.     

Total Synthesis of Sch 725674

A concise total synthesis of the macrolactone natural product Sch 725674 is accomplished starting from commercially available 2-deoxy-d-ribose. Pivotal reactions employed in the synthesis include the addition of 4-pentenylmagnesium bromide to the lactol derived from 2-deoxy-d-ribose, olefin cross metathesis and Yamaguchi macrolactonization.