Synthesis of the southern FGHI ring system of azaspiracid-1 and investigation into the controlling elements of C28- and C36-ketalization

Total Synthesis of Macrocyclic Dysoxylactam A

The total synthesis of dysoxylactam A, a novel 17-membered macrolactam with potent multi-drug-resistant reversing activities, has been achieved, starting from 4-pentene-1-al in a longest linear sequence of 17 steps and 9.5% overall yield. The key transformations consist of iterative aldol and ring-closing metathesis reactions for the construction of the stereochemically enriched polypropionate scaffold and the macrocycle, respectively.

Total Synthesis of Kanamienamide

Kanamienamide is a novel enol ether containing enamide with a single digit micromolar inhibitory activity against cancer cell lines. An efficient and convergent total synthesis of kanamienamide has been developed for the first time, which features a Cu-mediated amide coupling with vinyl iodide at the late stage. Other key transformations include Evans asymmetric alkylation, CBS asymmetric reduction, ring-closing metathesis reaction, and Stork-Zhao-Wittig olefination. This strategy is amenable for facile analogue preparation and SAR studies.

Stereoselective, Ag-Catalyzed Cyclizations To Access Polysubstituted Pyran Ring Systems: Synthesis of C1-C12 Subunit of Madeirolide A

The exploration into the scope of a silver-catalyzed cyclization (AgCC) of propargyl benzoates for accessing pyran ring systems has been reported. The impact of the degree of substitution, nature of the substitution on the carbon backbone/benzoate moiety, and stereochemistry has been evaluated. The application of this methodology to the synthesis of the C1-C12 southern fragment of madeirolide A is disclosed.

Direct asymmetric syntheses of chiral aldehydes and ketones via N-acyl chiral auxiliary derivatives including chiral Weinreb amide equivalents

This article covers N-acyl chiral auxiliary-based approaches to the asymmetric synthesis of enantiopure aldehydes and ketones. The use of diastereoisomerically pure N-acyl derivatives of chiral auxiliaries (including chiral Weinreb amide equivalents) and their conversion to the corresponding enantiopure aldehydes and ketones in a single synthetic operation by treatment with a hydride reducing agent or an organometallic reagent, respectively, are highlighted.

Synthesis of the spiroiminal moiety and approaches to the synthesis of marineosins A and B

A short and efficient synthesis of model spiroiminals that have the same stereochemistry as marineosins A and B, but different conformations, was carried out in six or seven steps from 6-methyltetrahydropyran-2-one. These spiroiminals were also prepared biomimetically by reduction of an enol ether. A more highly substituted spiroiminal with the same stereochemistry and conformation as marineosin A was prepared in 11 steps from parasorbic acid. A macrocyclic pyrrole lactone was prepared stereospecifically in 10 steps. A five-step sequence converted the lactone to a late hemi-iminal intermediate that has resisted the methylation and spiroiminal formation that would lead to marineosin A.

Amphidinolide B: total synthesis, structural investigation, and biological evaluation

The total syntheses of amphidinolide B1 and the proposed structure of amphidinolide B2 have been accomplished. Key aspects of this work include the development of a practical, non-transition-metal-mediated method for the construction of the C13-C15 diene, the identification of α-chelation and dipole minimization models for diastereoselective methyl ketone aldol reactions, the discovery of a spontaneous Horner-Wadsworth-Emmons macrocyclization strategy, and the development of a novel late stage method for construction of an allylic epoxide moiety. The originally proposed structure for amphidinolide B2 and diastereomers thereof display potent antitumor activities with IC50 values ranging from 3.3 to 94.5 nM against human solid and blood tumor cells. Of the different stereoisomers, the proposed structure of amphidinolide B2 is over 12-fold more potent than the C8,9-epimer and C18-epimer in human DU145 prostate cancer cells. These data suggest that the epoxide stereochemistry is a significant factor for anticancer activity.

Nickel-Catalyzed Regiodivergent Approach to Macrolide Motifs

A strategy for regiochemical reversal of reductive macrocyclizations of aldehydes and terminal alkynes has been developed. Using an advanced synthetic intermediate directed towards the methymycin/neomethymycin class of macrolides, selective endocyclization provides the natural twelve-membered ring series, whereas ligand alteration enables selective exocyclization to provide access to the unnatural eleven-membered ring series. The twelve-membered ring adduct was converted to 10-deoxymethynolide, completing an efficient total synthesis of this natural product.

Role of pseudoephedrine as chiral auxiliary in the "acetate-type" aldol reaction with chiral aldehydes; asymmetric synthesis of highly functionalized chiral building blocks

We have studied in depth the aldol reaction between acetamide enolates and chiral α-heterosubstituted aldehydes using pseudoephedrine as chiral auxiliary under double stereodifferentiation conditions, showing that high diastereoselectivities can only be achieved under the matched combination of reagents and provided that the α-heteroatom-containing substituent of the chiral aldehyde is conveniently protected. Moreover, the obtained highly functionalized aldols have been employed as very useful starting materials for the stereocontrolled preparation of other interesting compounds and chiral building blocks such as pyrrolidines, indolizidines, and densely functionalized β-hydroxy and β-amino ketones using simple and high-yielding methodologies.

Total synthesis of (+)-azaspiracid-1. An exhibition of the intricacies of complex molecule synthesis

The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.

Total synthesis of cytotoxic macrolide amphidinolide B1 and the proposed structure of amphidinolide B2

The first enantioselective total syntheses of cytotoxic macrolide amphidinolide B1 and the proposed structure for amphidinolide B2 have been accomplished. Key features of the syntheses include a diastereoselective aldol condensation, a spontaneous Wadsworth-Emmons macrocyclization and a directed epoxidation/elimination sequence.

Nitrile-Promoted Rh-Catalyzed Intermolecular Hydroacylation of Olefins with Salicylaldehyde

Rh-catalyzed intermolecular hydroacylation between salicylaldehyde and alkenylnitriles proceeded at room temperature to preferentially give normal-hydroacylated products. Addition of CH3CN and NaOAc accelerated the Rh-catalyzed hydroacylation of monoolefins to exclusively produce the normal-hydroacylated products under mild reaction conditions. Plausible mechanisms for the regioselections are also described.