Synthetic Study of Diversifolin: The Construction of 11-Oxabicyclo[6.2.1]undec-3-ene Core Using Ring-Closing Metathesis

Total Synthesis and Bioactivity Profile of (+)-Ieodomycins A and B and their Stereoisomers

Herein, we report the first- and second-generation syntheses of (+)-ieodomycins A and B and their stereoisomers via the late-stage elaboration of their conjugated E-diene side chains. Key steps for successful synthesis included Keck asymmetric allylation to introduce a hydroxyl group at the C5 position, consecutive Wipf's carboalumination modification, iodination, Sharpless asymmetric dihydroxylation, one-carbon homologation via cyanation, Mukaiyama lactonization, and Stille cross-coupling to form the conjugated E-diene moiety. Further, the preliminary in vitro bioactivity profile against various disease-related molecular targets and cell lines was investigated. Results indicated that compounds 30b and 30c, diastereoisomers of (+)-ieodomycin B (2), serve as α-glucosidase inhibitors, while compounds 30b and 30d inhibit the angiotensin-converting enzyme.

Enantioselective total synthesis of (+)-ieodomycin A, (+)-ieodomycin B, and their three stereoisomers

Enantioselective routes for the total synthesis of ieodomycins A & B, and three stereochemical analogues of ieodomycin B via a late-stage elaboration of the side chain.

Stereoselective Synthesis of Highly Substituted Tetrahydropyrans through an Evans Aldol-Prins Strategy

A direct and general method for the synthesis of naturally occurring 2,3,4,5,6-pentasubstituted tetrahydropyrans has been developed, employing β,γ-unsaturated N-acyl oxazolidin-2-ones as key starting materials. The combination of the Evans aldol addition and the Prins cyclization allowed the diastereoselective and efficient generation of the desired oxacycles in two fashions: a one-pot Evans aldol-Prins protocol, in which five new σ bonds and five contiguous stereocenters were straightforwardly generated, and a two-step version, which additionally permitted the isolation of β,γ-unsaturated alcohol precursors bearing an N-acyl oxazolidin-2-one in the α position. From these alcohols were also obtained halogenated pentasubstituted tetrahydropyrans as well as 2,3,4,5-tetrasubstituted tetrahydrofurans, shedding light on the mechanism of the process. Computational studies were consistent with the experimental findings, and this innovative Evans aldol-Prins strategy was performed for the preparation of a battery of more than 30 densely substituted tetrahydropyrans, unprecedentedly fused to a 1,3-oxazinane-2,4-dione ring, both in a racemic fashion and in an enantiomeric fashion. These novel molecules were successfully submitted to several transformations to permit simple access to a variety of differently functionalized tetrahydropyrans. Most of these unique molecules were evaluated for their antimicrobial activity against Gram-positive and Gram-negative bacteria and the yeast Candida albicans, and some structure-activity relationships were established.

Synthetic explorations of the briarane jungle: progress in developing a synthetic route to a common family of diterpenoid natural products

The briarane diterpenoids are a large family of marine natural products that have been primarily isolated from gorgonian octocorals around the world. Structurally, the family is characterized by a trans-fused bicyclo[8.4.0]tetradecane ring system containing a central, stereogenic, all-carbon quaternary carbon (C1) flanked by three additional stereocentres (C2, C10, C14). Many family members have demonstrated biological activity in numerous areas, including: cytotoxicity, anti-inflammatory, antiviral, antifungal, immunomodulatory and insect control. Despite their interesting structural properties and bioactivity, the briaranes have been largely overlooked by the synthetic community. However, in recent years, several research groups have reported progress toward developing a synthetic route to these natural products. Most of these efforts have focused on the stereoselective construction of the central C1-C2-C10-C14 stereotetrad. This review will discuss the various synthetic efforts aimed at the briarane diterpenoids along with the challenges that remain.