Enantioselective Synthesis of Pyranofuranone Moieties of Manoalide and Cacospongionolide B by Enzymatic and Chemical Approach

Marine natural products and related compounds in clinical and advanced preclinical trials

The marine environment has proven to be a very rich source of extremely potent compounds that have demonstrated significant activities in antitumor, antiinflammatory, analgesia, immunomodulation, allergy, and anti-viral assays. Although the case can and has been made that the nucleosides such as Ara-A and Ara-C are derived from knowledge gained from investigations of bioactive marine nucleosides, no drug directly from marine sources (whether isolated or by total synthesis) has yet made it to the commercial sector in any disease. However, as shown in this review, there are now significant numbers of very interesting molecules that have come from marine sources, or have been synthesized as a result of knowledge gained from a prototypical compound, that are either in or approaching Phase II/III clinical trials in cancer, analgesia, allergy, and cognitive diseases. A substantial number of other potential agents are following in their wake in preclinical trials in these and in other diseases.

Total Syntheses of (+)- and (−)-Cacospongionolide B, Cacospongionolide E, and Related Analogues. Preliminary Study of Structural Features Required for Phospholipase A2 Inhibition

The total syntheses of the antiinflammatory marine sponge metabolites (+)-cacospongionolide B and E are described. The pivotal steps in the synthetic route include a three-step sequence that couples the two main regions of the natural product, as well as generates the side chain dihydropyran ring. The activity of the synthetic analogues against bee venom phospholipase A2 suggests that the cacospongionolides have enantiospecific interactions with the enzyme that may be independent of the gamma-hydroxybutenolide moiety.

Synthesis of (+)-manoalide via a copper(I)-mediated 1,2-metalate rearrangement

An enantiospecific synthesis of the phospholipase A(2) inhibitor (+)-(4R)-manoalide is reported in which all 25 carbons of the sesterterpenoid skeleton are constructed from 3-furaldehyde, trimethylalane, oxirane, CO, beta-ionone, and propargyl bromide. The overall yield for the longest linear sequence (12 steps) is 12%. Key steps include (a) a zirconium-catalyzed carboalumination reaction to construct the C10-C11 trisubstituted alkene, (b) a Cu(I)-mediated 1,2-metalate rearrangement to construct the C6-C7 trisubstituted alkene, (c) a Sharpless kinetic resolution to secure the (4R)-stereochemistry, (d) generation of a 5-stannyl-2,3-dihydrofuran by Mo-catalyzed cycloisomerization of a homopropargylic alcohol, and (e) construction of the hydroxyfuranone ring by photooxidation of a silylfuran.

Total Syntheses of (+)- and (−)-Cacospongionolide B: New Insight into Structural Requirements for Phospholipase A2 Inhibition

The first total synthesis of the antiinflammatory marine sponge metabolite (+)-cacospongionolide B has been accomplished in 12 linear steps. The pivotal transformations include a three-step sequence coupling the two main regions of the natural product as well as generating the side chain dihydropyran ring. The activity of the synthetic analogues against bee venom phospholipase A(2) suggests that cacospongionolide B has an enantiospecific interaction with the enzyme that is independent of the gamma-hydroxybutenolide moiety.