Studies directed toward the synthesis of the massileunicellins

Secondary Metabolites from Gorgonian Corals of the Genus Eunicella: Structural Characterizations, Biological Activities, and Synthetic Approaches

Gorgonian corals, which belong to the genus Eunicella, are known as natural sources of diverse compounds with unique structural characteristics and interesting bioactivities both in vitro and in vivo. This review is focused primarily on the secondary metabolites isolated from various Eunicella species. The chemical structures of 64 compounds were divided into three main groups and comprehensively presented: a) terpenoids, b) sterols, and c) alkaloids and nucleosides. The observed biological activities of depicted metabolites with an impact on cytotoxic, anti-inflammatory, and antimicrobial activities were reviewed. The most promising biological activities of certain metabolites point to potential candidates for further development in pharmaceutical, cosmetic, and other industries, and are highlighted. Total synthesis or the synthetic approaches towards the desired skeletons or natural products are also summarized.

Total synthesis of (±)-phomactin A. Lessons learned from respecting a challenging structural topology

Our struggles and ultimate success in achieving a total synthesis of phomactin A are described. Our strategy features an intramolecular oxa-[3 + 3] annulation to construct its unique ABD-tricyclic manifold. Although the synthesis would constitute a distinctly new approach with the 12-membered D-ring of phomactin A being assembled simultaneously with the 1-oxadecalin at an early stage, the ABD-tricycle represents a unique structural topology that would pose a number of unprecedented challenges. One challenge concerned elaborating this tricycle to have oxygenation at the proper carbon atoms. To overcome this, we would utilize a Kornblum-DeLaMare ring-opening of a peroxide bridge as well as a challenging late-stage 1,3-allylic alcohol transposition. Further, the structural intricacies of the ABD-tricycle were uncovered by a conformational analysis that would be critical for the C5a-homologation.

Studies directed toward the synthesis of the massileunicellins. 2

The fully substituted hydroisobenzofuran core of the massileunicellins containing 8 contiguous stereocenters was prepared in 12 steps from (S)-(+)-carvone. Noteworthy elements of the synthesis include a one-step oxidative rearrangement/epoxidation, a novel stereoselective directed reduction of a keto diol, and a directed hydrogenation of a congested tetrasubstituted alkene.

Enantiospecific synthesis of the cubitane skeleton

The fully substituted 12-membered macrocycle of the cubitane-type diterpenoids has been assembled in an enantioselective manner following a novel "bridge-and-cut" strategy. Hydroxyalkylation of (S)-carvone afforded a carvonylgeraniol, which underwent transannular cyclization on treatment with samarium diiodide in THF. Fragmentation of one of the shorter bridges of the resulting [8.2.2]bicycle liberated the 12-membered ring with the desired cis-arrangement of the isopropenyl side chains.

Synthesis and anticancer activity of sclerophytin-inspired hydroisobenzofurans

Three structurally related sets of hydroisobenzofuran analogs of sclerophytin A were prepared in three or four steps from (S)-(+)-carvone via an aldol-cycloaldol sequence. The most potent members of each set of analogs exhibited IC(50)'s of 1-3 microM in growth inhibitory assays against KB3 cells. The NCI 60-cell line 5-dose assay for analog 6h revealed a GI(50)=0.148 microM and LC(50)=9.36 microM for the RPMI-8226 leukemia cell line, and a GI(50)=0.552 microM and LC(50)=26.8 microM for the HOP-92 non-small cell lung cancer cell line.

Total synthesis of phomactin A

A total synthesis of (+/-)-phomactin A is described to highlight the final completion of a complex natural product target that had commenced with an intramolecular oxa-[3 + 3] annulation strategy in the construction of the ABD-tricycle. These efforts reveal structural intricacies of this ABD-tricycle with an illustrative example being the conformational analysis that was ultimately critical for the C5a-homolgation.

Approach to the synthesis of cladiell-11-ene-3,6,7-triol

[reaction: see text] The synthesis of an advanced intermediate in the synthesis of the title compound has been achieved. Key steps include an Ireland-Claisen rearrangement to install the C7 tertiary alcohol stereocenter, an SN2' reaction of an alkoxymethyl Cu reagent, and a diastereoselective Re-catalyzed allylic alcohol transposition.