Total synthesis of (+)-spongistatin 1. An effective second-generation construction of an advanced EF Wittig salt,fragment union,and final elaboration

A stereocontrolled, total synthesis of (+)-spongistatin 1 (1) has been achieved. Union of a second-generation EF Wittig salt (+)-3 with the advanced ABCD aldehyde (-)-4, followed by regioselective macrolactonization and global deprotection afforded (+)-spongistatin 1 (1). The longest linear sequence, 29 steps, proceeded in 0.5% overall yield.     

Spongipyran synthetic studies. Evolution of a scalable total synthesis of (+)-spongistatin 1

Three syntheses of the architecturally complex, cytotoxic marine macrolide (+)-spongistatin 1 (1) are reported. Highlights of the first-generation synthesis include: use of a dithiane multicomponent linchpin coupling tactic for construction of the AB and CD spiroketals, and their union via a highly selective Evans boron-mediated aldol reaction en route to an ABCD aldehyde; introduction of the C(44)-C(51) side chain via a Lewis acid-mediated ring opening of a glucal epoxide with an allylstannane to assemble the EF subunit; and final fragment union via Wittig coupling of the ABCD and EF subunits to form the C(28)-C(29) olefin, followed by regioselective Yamaguchi macrolactonization and global deprotection. The second- and third-generation syntheses, designed with the goal of accessing 1 g of (+)-spongistatin 1 (1), maintain both the first-generation strategy for the ABCD aldehyde and final fragment union, while incorporating two more efficient approaches for construction of the EF Wittig salt. The latter combine the original chelation-controlled dithiane union of the E- and F-ring progenitors with application of a highly efficient cyanohydrin alkylation to append the F-ring side chain, in conjunction with two independent tactics to access the F-ring pyran. The first F-ring synthesis showcases a Petasis-Ferrier union/rearrangement protocol to access tetrahydropyrans, permitting the preparation of 750 mg of the EF Wittig salt, which in turn was converted to 80 mg of (+)-spongistatin 1, while the second F-ring strategy, incorporates an organocatalytic aldol reaction as the key construct, permitting completion of 1.009 g of totally synthetic (+)-spongistatin 1 (1). A brief analysis of the three syntheses alongside our earlier synthesis of (+)-spongistatin 2 is also presented.     

Spongistatin synthetic studies. evolution of a scalable synthesis for the EF fragment of (+)-Spongistatin 1 exploiting a Petasis-Ferrier union/rearrangement tactic

[structure: see text] An efficient, stereocontrolled, and scalable second-generation synthesis of (+)-3, an advanced EF subtarget for the total synthesis of (+)-spongistatin 1, has been achieved. Highlights of the strategy include preparation of the F-ring pyran via a Petasis-Ferrier union/rearrangement sequence and installation of the chlorodiene side chain employing a cyanohydrin alkylation. The longest linear sequence, 26 steps, proceeds in 8.3% overall yield.     

Design, synthesis, and biological evaluation of diminutive forms of (+)-spongistatin 1: lessons learned

The design, synthesis, and biological evaluation of two diminutive forms of (+)-spongistatin 1, in conjunction with the development of a potentially general design strategy to simplify highly flexible macrocyclic molecules while maintaining biological activity, have been achieved. Examination of the solution conformations of (+)-spongistatin 1 revealed a common conformational preference along the western perimeter comprising the ABEF rings. Exploiting the hypothesis that the small-molecule recognition/binding domains are likely to comprise the conformationally less mobile portions of a ligand led to the design of analogues, incorporating tethers (blue) in place of the CD and the ABCD components of the (+)-spongistatin 1 macrolide, such that the conformation of the retained (+)-spongistatin 1 skeleton would mimic the assigned solution conformations of the natural product. The observed nanomolar cytotoxicity and microtubule destabilizing activity of the ABEF analogue provide support for both the assigned solution conformation of (+)-spongistatin 1 and the validity of the design strategy.     

Spongipyran synthetic studies. Total synthesis of (+)-spongistatin 2

Evolution of a convergent synthetic strategy to access (+)-spongistatin 2 (2), a potent cytotoxic marine macrolide, is described. Highlights of the synthesis include: development of a multicomponent dithiane-mediated linchpin union tactic, devised and implemented specifically for construction of the spongistatin AB and CD spiro ring systems; application of a Ca^II ion controlled acid promoted equilibration to set the thermodynamically less stable axial-equatorial stereogenicity in the CD spiroketal; use of sulfone addition/Julia methylenation sequences to unite the AB and CD fragments and introduce the C(44)-C(51) side chain; and fragment union and final elaboration to (+)-spongistatin 2 (2) exploiting Wittig olefination to unite the advanced ABCD and EF fragments, followed by regioselective Yamaguchi macrolactonization and global deprotection. Correction of the CD spiro ring stereogenicity was subsequently achieved via acid equilibration in the presence of Ca^II ion to furnish (+)-spongistatin 2 (2). The synthesis proceeded with a longest linear sequence of 41 steps.     

Total synthesis of myxothiazols, novel bis-thiazole beta-methoxyacrylate-based anti-fungal compounds from myxobacteria

Convergent total syntheses of myxothiazols A and Z are described. The syntheses are based on elaboration of the (S)-E,E-diene thioamide 22, conversion of 22 into the bis-thiazole 27 and Wittig reactions between 27c and the aldehyde 30. The substituted beta-methoxyacrylate aldehyde 30 was produced via an Evans asymmetric aldol protocol or via the 2H-pyran-2-one 31. An E-selective Wittig reaction between the ylide derived from the phosphonium salt 27c and the (+)-aldehyde 30 led to (+)-myxothiazol Z (1b), and a corresponding reaction with the (+/-)-acrylamide aldehyde 44 gave (+/-)-myxothiazol A (1a). Complementary studies led to synthesis of the ester 47b, corresponding to myxothiazol R and myxothiazol S.     

Total synthesis of pyrrolidine alkaloid, Radicamine-B via Stille coupling

Total synthesis of (−) Radicamine-B is achieved in eight steps from (R)-(+)-Garner aldehyde in a stereoflexible manner involving Stille coupling and one-pot domino epoxidation-pyrrolidine formation as key steps.     

Formal enantioselective synthesis of (+)-compactin

[reaction: see text] The challenging structural features and important biological activity of (+)-compactin (1) explain the substantial synthetic interest that it has generated. We report a novel enantioselective approach to the advanced intermediate 2a, which constitutes a formal synthesis of (+)-1. The sequence utilizes MacMillan's organocatalytic Mukaiyama-Michael reaction, which stereoselectively adds the silyloxyfuran 6 to alpha,beta-unsaturated aldehyde 7. The chirality generated in this reaction guides the formation of the other three consecutive stereocenters found in 2a.     

Total synthesis of (+)-13-deoxytedanolide

In this communication we describe the first total synthesis of (+)-13-deoxytedanolide, an architecturally complex marine macrolide possessing significant antitumor activity. The cornerstone of the synthesis comprises a highly convergent dithiane coupling used to construct the carbon skeleton, followed by a novel use of the Evans-Tishchenko reduction to oxidize the C(1) aldehyde to an ester in the presence of the oxidatively labile dithiane.     

Stereoselective synthesis of (+)-boronolide

The delta-lactone boronolide (+)-1, a pharmacologically active, naturally occurring product, has been synthesized in enantiopure form with L-erythrulose as the chiral starting material. The key steps of the synthesis were a highly stereoselective aldol-reduction one-pot sequence, an indium-mediated diastereoselective aldehyde allylation, and a ring-closing metathesis.     

Enantioselective syntheses of (+)-xylarenal A and ent-xylarenal A

[reaction: see text] The total synthesis of the sesquiterpenoid xylarenal A is reported. This first synthetic entry to an eremophilane terpenoid with an exocyclic vinyl aldehyde unit involves the use of the bicyclic enone (+)-3, which after a gamma-oxidation and alpha'-allylation leads to the formation of the ketone (+)-8. After its acylation, an oxidative cleavage of the allyl side chain followed by alpha-methylenation of the resulting aldehyde gives (+)-xylarenal A (1). The synthesis of (-)-xylarenal A from (-)-3 is also reported. Moreover, the first total synthesis of the trinoreremophilane (+)-1alpha-hydroxyisoondetianone (5) is described.     

An efficient synthesis of dexlansoprazole employing asymmetric oxidation strategy

An alternative and scalable synthesis of dexlansoprazole ((R)-(+)-1); the (R)-enantiomer of Lansoprazole with an enantiomeric excess of >99.8% is presented.     

First enantiospecific total synthesis of the important biogenetic intermediates, (+)-polyneuridine and (+)-polyneuridine aldehyde, as well as 16-epi-vellosimine and macusine A

The first enantiospecific total synthesis of the alkaloids 16-epi-vellosimine (1), (+)-polyneuridine (2), (+)-polyneuridine aldehyde (3), and macusine A (4) is reported. The key oxidation was accomplished with the Corey-Kim reagent to provide the important biogenetic intermediates, 16-epi-vellosimine (1) and polyneuridine aldehyde (3), the latter of which is required for the conversion of the sarpagan skeleton into the ajmalan system in the biosynthesis of quebrachidine. [reaction: see text].     

Total synthesis and correct absolute configuration of malyngamide U

The enantioselective synthesis of the previously proposed structure of malyngamide U (1) was accomplished in 18 steps from (S)-(+)-carvone. The key steps involved a hydroxymethylation of (S)-(+)-carvone and an asymmetric Henry reaction of aldehyde (+)-5, as well as condensation with the acid 3. The 1H and 13C NMR data of the synthetic compound 1 were not consistent with the data of the reported malyngamide U. The C-2' epimer of compound 1 was therefore synthesized by a similar reaction sequence. While the NMR data of C-2' epimer 23 were in full agreement with those of the reported product, the discrepancy in the specific rotation data suggested the correct structure of malyngamide U should be structure 2, in which the absolute configuration of the amine part was enantiomeric with that in compound 23. Then the correct absolute configuration of revised malyngamide U (2) was confirmed by the similar synthesis from (R)-(-)-carvone.     

A concise enantioselective synthesis of (+)-goniodiol and (+)-8-methoxygoniodiol via Co-catalyzed HKR of anti-(2SR, 3RS)-3-methoxy-3-phenyl-1, 2-epoxypropane

A short, enantioselective synthesis of (+)-goniodiol and (+)-8-methoxygoniodiol, cytotoxic styryllactones, has been achieved in high optical purities (99% ee). The strategy employs Co-catalyzed HKR of racemic anti-(2SR, 3RS)-3-methoxy-3-phenyl-1, 2-epoxypropane and Lewis acid-mediated diastereoselective allylation of aldehyde as chiral inducing key reactions.     

Asymmetric synthesis of a dopamine D1 agonist,dihydrexidine from d-serine

A scalable asymmetric synthesis of trans-2-amino-6,7-dimethoxy-1-phenyltetralin 2 and its N-nosyl derivative 12 have been achieved from Garner aldehyde derived from easily available d-serine using a stereoselective PhMgBr addition, Wittig reaction and TFA-mediated Friedel–Crafts cyclization as the key steps. The synthesis of dihydrexidine is accomplished from the N-nosyl-2-amino-1-phenyltetralin 12.     

Scalable total synthesis of horsfiequinone A

Starting from two commercially available substrates, methoxyhydroquinone and piperonyl alcohol, a scalable four-step total synthesis of horsfiequinone A was developed. The notable feature of the synthesis is the application of two continuous sequential transformations. Namely, the key aldehyde 9 and horsfiequinone A were prepared via scalable Wittig/hydrolysis and Wittig/catalytic hydrogenation/oxidation sequences, respectively. Importantly, the synthetic route required only three recrystallizations and one column chromatography purification step.     

The synthesis of (+)-allopumiliotoxin 323B'

This paper describes the synthesis of (+)-allopumiliotoxin 323B' (1) using the intramolecular [3 + 2]-cycloaddition reaction of the (Z)-N-alkenylnitrone 4. This synthesis began with (R)-tert-butyl-3-hydroxy-pent-4-enoate [(R)-13] which was obtained by enzymatic resolution with Amano PS lipase. A series of manipulations gave intermediate 17 and in situ coupling with 4-benzoyloxybutanal lead to the (Z)-N-alkenylnitrone 4 which underwent an intramolecular [3 + 2]-cycloaddition reaction to give the isoxazolidine 3 as the major cycloadduct. Isoxazolidine 3 provided the piperidinone 24 which upon diastereofacial selective addition of MeMgBr gave the required tertiary alcohol 25. Formation of the indolizidine core 2 was achieved by an intramolecular S(N)2 reaction. The side chain was assembled from a Wittig reaction between the phosphorane 8 and the enantiomerically pure aldehyde 9. Further modifications afforded the aldehyde 7 which underwent an aldol condensation with the potassium enolate of the indolizidone core 2. Dehydration gave the enone 37 which was converted into the anti-diol 38 by intramolecular hydride reduction. Finally, deprotection of the BOM protecting group gave (+)-allopumiliotoxin 323B' (1).     

Total synthesis of (+)-asteltoxin

A convergent synthesis of (+)-asteltoxin (1) has been achieved by the Horner-Emmons olefination of bis(tetrahydrofuran) aldehyde 53 and alpha-pyrone phosphonate 5. A key step features the stereoselective construction of a sterically congested quaternary center embedded in the densely functionalized bis(tetrahydrofuran) subunit by a Lewis acid-catalyzed, pinacol-type rearrangement of an epoxy silyl ether. This pivotal rearrangement methodology parallels the proposed biosynthetic pathway of 1 and is ripe for applications to the stereocontrolled synthesis of structurally complex natural products.     

Concise asymmetric synthesis of (R)-(+)-tanikolide

A highly stereoselective total synthesis of (R)-(+)-tanikolide, a δ-lactonic marine natural product, was accomplished in seven steps from easily available starting materials with a 51% overall yield. An asymmetric synthesis of an α-hydroxy aldehyde having a stereogenic quaternary center, by the use of (S)-2-(anilinomethyl)pyrrolidine as a chiral auxiliary, was employed in a key step.