Towards the total synthesis of amphidinolide E: an enantioselective synthesis of C12-C29 fragment

An enantioselective synthesis of the C12-C29 fragment of amphidinolide E is described. Key transformations include an intramolecular mercuriocyclization reaction, stereoselective introduction of methyl group at the C2 position, and Stille coupling for the introduction of the diene side chain.     

Stereoselective synthesis of the densely functionalized C1-C9 fragment of amphidinolides C and F

The synthesis of the C1-C9 subunit of amphidinolides C and F is described. Key steps include tandem Sharpless asymmetric dihydroxylation-S_N2 cyclization reaction, Lewis acid-mediated epoxide opening, Wittig reaction, and Wacker oxidation.     

Synthesis of the C(18)-C(34) fragment of amphidinolide C and the C(18)-C(29) fragment of amphidinolide F

A convergent synthesis of the C(18)-C(34) fragment of amphidinolide C and the C(18)-C(29) fragment of amphidinolide F is reported. The approach involves the synthesis of the common intermediate tetrahydrofuranyl-β-ketophosphonate via cross metathesis, Pd(0)-catalyzed cyclization, and hydroboration-oxidation. The β-ketophosphonate was coupled to three side chain aldehydes using a Horner-Wadsworth-Emmons (HWE) olefination reaction to give dienones, which were reduced with l-selectride to give the fragments of amphidinolide C and F.     

Synthesis of the C11-C29 fragment of amphidinolide F

[reaction: see text] An efficient synthesis of the C(11)-C(29) fragment 31 of amphidinolide F has been accomplished via a diastereoselective [3 + 2]-annulation reaction of allylsilane 5 and ethyl glyoxylate to prepare the key tetrahydrofuran 15 and a highly stereoselective methyl ketone aldol reaction to generate the C(11)-C(16) segment.     

Synthetic studies toward amphidinolide B1: synthesis of the C9-C26 fragment

[reaction: see text] The synthesis of the C9-C26 portion of amphidinolide B1 is described. A Fleming allylation followed by elimination was employed for the construction of the C13-C15 diene portion. Sharpless asymmetric dihydroxylation was utilized for regioselective functionalization of a styrene-derived alkene, in the presence of the C13-C15 diene functionality. A highly diastereoselective aldol reaction was developed to establish the C18 stereochemistry.     

Synthetic studies of incednine: synthesis of C1-C13 pentaenoic acid segment

Stereoselective synthesis of the C1-C13 pentaenoic acid segment (4) of the novel antibiotic incednine (1) is described.     

Synthetic studies on neomarinone: practical and efficient stereoselective synthesis of the side chain

A practical and efficient stereoselective synthesis of the side chain of neomarinone is reported. The synthesis was achieved in six steps (41% overall yield) from 2-methyl-2-cyclohexenone. The key step is a novel stereoselective 1,4-conjugate addition/enolate alkylation by an epoxide-opening reaction.     

Gram scale synthesis of the C(18)-C(34) fragment of amphidinolide C

The synthesis of the C(18)-C(34) fragment of amphidinolide C has been achieved via two routes, culminating in both the shortest (11 steps) and highest yielding (26% overall yield) approaches to this segment. The highly convergent approach will facilitate the synthesis of analogues, including the C(18)-C(29) fragment of amphidinolide F. Synthetic highlights include the selective methylation of a diyne, and the highly efficient use of a second generation cobalt catalyst in the Mukaiyama oxidative cyclization to form the trans-THF ring.     

Synthesis of the C3-C18 fragment of amphidinolides G and H

A synthesis of an amphidinolides G and H C3-C18 subunits is reported. The C10-C18 segment 4 was prepared by a Negishi cross-coupling, whereas the synthesis of the C3-C9 fragment 5 employed an asymmetric cyanosilylation as the key step. The two segments were coupled by lithiation of iodide 4 and trapping of the anion with amide 5. The allylic epoxide moiety could be synthesized from the protected anti- mesylate 22.     

Improved synthesis of C8-C20 segment of pectenotoxin-2

The C8-C20 segment of pectenotoxin-2 was efficiently synthesized in 16% overall yield in 22 steps from l-malic acid via an improved route.     

Synthetic studies on antascomicin A: construction of the C18-C34 fragment

Stereoselective synthesis of the C18-C34 fragment of antascomicin A is described. Construction of the C27-C34 carbocycle moiety was achieved via catalytic Ferrier carbocylization and Johnson-Claisen rearrangement, which was converted to iodide 2 by use of asymmetric alkylation and Sharpless epoxidation as key transformations. Coupling of iodide 2 and sulfone 3 furnished the C18-C34 fragment.     

Synthetic studies on borrelidin: enantioselective synthesis of the C1-C12 fragment

[structure: see text] An efficient, enantioselective synthesis of the C1-C12 fragment 2 of borrelidin is presented. Construction of the "skipped" polymethylene chain of 2 was accomplished by iteration of Myers' alkylation, while formation of the C3 stereocenter was achieved by Roush's asymmetric allylboration methodology.     

Efficient synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F

The synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F was achieved by using a vinyloguous Mukaiyama aldol reaction on a chiral aldehyde with a silyloxyfuran and by using a C-glycosylation of a lactol derivative with an acetyl oxazolidinethione. From the available chiral acetonide-glyceraldehyde, all the stereogenic centers were perfectly induced along the synthesis. The C(1)-C(9) fragment was synthesized as a vinyl stannane at C(9) in 10 steps, with 16% yield.     

Stereoselective synthesis of the C3-C15 fragment of callyspongiolide

The synthesis of C3-C15 fragment of callyspongiolide, a 14-membered macrolides isolated from the marine sponge Callyspongia sp., which was collected from the Indonesia, is reported. Highlights of the synthesis include construction of E-olefin through Julia-Kocienski olefination, Brown asymmetric allylation and base-induced elimination reactions for propargyl alcohol synthesis.     

Synthetic studies of venturicidins: stereoselective synthesis of the C15-C27 segment based on two types of stereospecific epoxide opening reactions

The C15-C27 segment of venturicidins was stereoselectively synthesized by using two types of stereospecific methyl substitution reactions of epoxides and subsequent stereocontrolled methylation reactions of lactone derivatives as the key steps.     

Synthetic studies on goniodomin A: convergent assembly of the C15-C36 segment via palladium-catalyzed organostannane-thioester coupling

A stereocontrolled convergent synthesis of the C15-C36 segment of goniodomin A, a potent anti-angiogenic marine polyether macrolide, has been achieved using Stille-type cross-coupling reaction of a vinylstannane and a thioester as a key segment assembly process.     

Total synthesis of naturally occurring 5,6,7- and 5,7,8-trioxygenated coumarins

The synthesis of five naturally occurring polyoxygenated coumarins is described. It concerns two 5,6,7-trioxygenated coumarins, i.e., 6-hydroxy-5,7-dimethoxycoumarin (fraxinol) 1 and 5,6,7-trimethoxycoumarin 2, and three 5,7,8-trioxygenated coumarins, i.e., 8-hydroxy-5,7-dimethoxycoumarin (leptodactylone) 3, 5,7,8-trimethoxycoumarin 4 and 8-(3-methyl-2-butenyloxy)-5,7-dimethoxycoumarin (artanin) 5. Key feature of the synthetic pathway is the synthesis of suitable tetraoxygenated benzaldehydes, which are then converted to the corresponding coumarins via a Wittig reaction.     

Synthetic studies on reidispongiolide A, an actin-depolymerizing marine macrolide: synthesis of C11-C22 and C23-C35 segments

The C11-C22 and C23-C35 segments 2 and 3 of reidispongiolide A (1), an actin-depolymerizing marine macrolide, were synthesized enantioselectively in 12 steps from (R)-glycidyl trityl ether and in 12 steps from chiral ketone 15, respectively.     

Synthetic studies on the DEF-rings of FR182877 and hexacyclinic acid

A synthesis of model DEF-rings of the polyketide anti tumor natural products FR182877 and hexacyclinic acid has been achieved. The key steps in the synthesis are an intramolecular Pd(0) catalyzed allylic substitution reaction, which was used to generate a 9-membered carbocycle, and a novel transannular iodocyclization reaction which furnished the DF-rings of both natural products.