Functionalized azirine based scaffolds as endothelin inhibitors for the selective anti-angiogenic activity.

Anti-angiogenic therapy has long been used as an adjunct therapy for the resolution of tumor burden. The current findings describe the synthesis of novel marine-based azirine-containing compounds that exhibit anti-angiogenic mediated anti-tumor activity. Azirine-2-carboxylate inhibited HUVEC-mediated tubulogenesis without causing cell death in a dose-dependent manner. Ex-vivo CAM, in-vivo Matrigel implantation, and ear angiogenesis experiments have all shown that azirine-2-carboxylate effectively inhibits angiogenesis. Furthermore, azirine-2-carboxylate inhibits the migration of ECs without disrupting the preformed tubule network. Azirine-2-carboxylate had adequate intramuscular systemic exposure and inhibited tumor growth in a xenograft mouse model. DARTS analysis, competitive binding assay, and gene expression investigations revealed that azirine-2-carboxylate inhibits endothelin-1-mediated angiogenesis. Overall, the discovery of azirine-2-carboxylate demonstrated a potent inhibition of angiogenesis targeting ET1 and a possible application in anti-angiogenic therapy.

Total synthesis of remdesivir.

Remdesivir, the first drug approved by the FDA to treat COVID-19, is in high demand for patients infected with the SARS-CoV-2 virus. Herein, we report a facile approach minimizing the protecting group manipulations to afford remdesivir in good overall yield.

Tandem Addition/Electrocyclization/Benzylation of Alkyl Aryl-1,3-dienes and Aromatic Aldehydes: Access to Highly Substituted Indenes.

BF3·Et2O-mediated synthesis of multisubstituted indenes from alkyl aryl-1,3-dienes and aromatic aldehydes through tandem addition/4π-electrocyclization/benzylation via tetrahydroindeno-oxepine/quinone methide followed by an intramolecular 1,6-hydride transfer is described. This novel reaction pathway is established by the isolation of potential intermediates and with the support of deuterium-labeling studies. In addition, the generality of this method is demonstrated by reacting various aromatic aldehydes, which ascertains the role of the electronic effect of aldehydes in the formation of indene derivatives and tetrahydroindeno-oxepines.

Stereoselective Access to the Core Structure of Macroline-Type Indole Alkaloids: Total Synthesis of Macroline and Alstomicine.

Rapid synthesis of the pentacyclic core structure of macroline-type indole alkaloids, and its application in the total synthesis of macroline and alstomicine is described. The core structure was accomplished in a highly stereocontrolled manner via two key steps, Ireland-Claisen rearrangement and Pictet-Spengler cyclization, commencing from a readily available starting material l-tryptophan, which obviated the need of a particular chiral source as an external catalyst, reagent, or internal auxiliary.

Nazarov Cyclization and Tandem [4 + 2]-Cycloaddition Reactions of Donor-Acceptor Cyclopropanes.

The development of aryl vinyl/divinyl donor-acceptor cyclopropanes (DACs) as novel Nazarov cyclization (NC) precursors is described. The 1,3-zwitterion, generated from DACs embedded in the divinyl framework, acts as a pentadienyl cation, a requisite for Nazarov cyclization. A cyclic allyl cation in the course of NC was trapped with external nucleophiles to provide an interrupted NC product. Indeed, an allyl cation in this reaction is analogous to a 1,4-zwitterion that on reaction with dipolarophiles provided an easy access to substituted pyrans with excellent yield and diastereoselectivity via NC followed by a formal [4 + 2] cycloaddition.

Nazarov cyclization of divinyl ketones bearing an ester group at the ß-position: a remarkable effect of α-substitution and alkene geometry on regioselectivity.

The Nazarov cyclization of divinyl ketones with an ester at the ß-position was examined with particular reference to where the cyclic double bond forms. We observed unprecedented regioselectivity, dictated by the subtle substitution patterns at the α-position and alkene geometry of α,ß and mostly, this selectivity is regardless of substitutions at α'- and ß'-positions. The major implications of these observations are an aromatic group at the α-position with E-olefin geometry provides a cyclopentenone in which the double bond is not in conjugation with an ester, whereas Z-olefin provides a cyclopentenone in which the double bond is in conjugation with an ester; and divinyl ketones bearing an ester group at the ß-position and an alkyl group at the α-position with E-olefin geometry provide a cyclopentenone in which the double bond is in conjugation with the ester.

Nazarov cyclization of dienylaziridines: synthesis of cyclopentadienyl/hydrinedienyl/indenyl glycines.

Cyclopentadienyl, hydrinedienyl, and indenyl glycines were synthesized using dienylaziridines as Nazarov cyclization precursors for the first time. Several substrates were synthesized to demonstrate the compatibility of this reaction. Asymmetric synthesis of these amino acids was also developed to show the additional scope of this method.

Nazarov cyclization of divinyl and arylvinyl epoxides: application in the synthesis of resveratrol-based natural products.

New variation in the Nazarov cyclization has been developed by preparing divinyl and arylvinyl epoxides as pentadienyl cation precursors for the first time. Highly substituted cyclopentadienes, hydrindienes, and indenes were synthesized to demonstrate the compatibility of this reaction with substrates bearing a variety of substitutions and having different types of epoxides. Application of this method in the synthesis of resveratrol-based natural products was also demonstrated.

Total synthesis of gonytolides C and G, lachnone C, and formal synthesis of blennolide C and diversonol.

The first stereoselective total synthesis of gonytolide C, which is a monomeric unit of an innate immune promoter gonytolide A, has been accomplished from the aldol reaction between acetophenone derived from orcinol and butyrolactone containing α-keto ester followed by the excellent diastereoselective intramolecular cyclization. The first total synthesis of gonytolide G has been achieved by the oxidation of benzylic methyl in gonytolide C. Additionally, total synthesis of lachnone C and a formal synthesis of blennolide C and diversonol have been achieved by this synthetic method.

Total synthesis of varitriol, varioxirane, and enantiomer of the proposed biosynthetic precursor.

The first stereoselective total synthesis of varioxirane was accomplished, and the proposed biosynthetic pathway was supported by converting varioxirane to (+)-varitriol. The first total synthesis of enantiomer of the proposed biosynthetic precursor, (1E,3S,4R,5E)-1-(2-(hydroxymethyl)-3-methoxyphenyl)hepta-1,5-diene-3,4-diol, was also achieved by utilizing the unreacted allylic alcohol obtained during the Sharpless kinetic resolution step. Other key steps include the Horner-Wadsworth-Emmons reaction and the diastereoselective reduction of α,ß-unsaturated ketone to its corresponding alcohol.

Total synthesis and absolute configuration of curvularides A-E.

The first total synthesis of curvularides A-E, isolated from a culture broth of the endophytic fungus Curvularia geniculata, is described. The divergent total synthesis reported herein confirmed the absolute configurations of curvularides A-E and supported that these natural products might be obtained from a common biosynthetic pathway. The key steps involved in the synthesis were the diastereoselective hydrogenation of exo-methylene-γ-butyrolactone to α-methyl-γ-butyrolactone, Sharpless kinetic resolution, Sharpless asymmetric epoxidations, and intramolecular and intermolecular epoxide openings.

Total synthesis and stereochemical revision of acortatarins A and B.

A first total synthesis of acortatarins A, B, and an enantiomer of the proposed structure of acortatarin B is described by using readily available d-sugars. This convergent total synthesis revealed the revision of the absolute configuration of acortatarin A and structural revision of acortatarin B. The key steps involved are regioselective epoxide opening with deprotonated 2,5-disubstituted pyrrole and spiroketalization.