Total Synthesis and Configurational Assignment of Ascospiroketal A

Synthesis and Bioactivity of Thiocarboxylic A and Derivatives

The Penicillium metabolite thiocarboxylic A (1a) and three close analogues were synthesized in 14 steps. The stereogenic elements were installed via stereoselective Sharpless epoxidation, (E)-selective reduction of a dibromide, and a Suzuki cross coupling. Thiocarboxylic A (1a) was obtained in 6% overall yield. The synthetic product and the natural isolate differed markedly in their specific rotations and antibiotic activities against Escherichia coli and Staphylococcus aureus. This modular synthetic route should be flexible enough to allow the synthesis of other natural and non-natural 3-methoxycarbonyldihydrofuran-4-ones for biological studies.

Synthesis and Bioactivity of Ophiofuranones A and B

Ophiofuranones A and B, metabolites of the fungus Ophiosphaerella korrae, were synthesized in 16 steps and 12%/22% yield. The stereogenic centers were established by Sharpless dihydroxylations and epoxidation, the 1,3-dienes via Wittig or HWE olefinations. The rings were closed through Knoevenagel-type condensation and lactonization. The ophiofuranones proved nontoxic at relevant concentrations against tumor cells, fibroblasts, and various bacteria and fungi. Ophiofuranone A and the monocyclic precursors 4 were weakly active against microbial biofilms.

Total synthesis of biselide A

A total synthesis of the marine macrolide biselide A is described that relies on an enantiomerically enriched α-chloroaldehyde as the sole chiral building block. Several strategies to construct the macrocycle are presented including a macrocyclic Reformatsky reaction that ultimately provides access to the natural product in a longest linear sequence of 18 steps. Biological testing of synthetic biselide A suggests this macrolide disrupts cell division through a mechanism related to the regulation of microtubule cytoskeleton organization. Overall, this concise synthesis and insight gained into the mechanism of action should inspire medicinal chemistry efforts directed at structurally related anticancer marine macrolides.

Synthesis of enantioenriched α-heteroatom functionalised aldehydes by chiral organocatalysis and their synthetic applications

Asymmetric organocatalysis is a versatile method for the enantioselective α-functionalisation of aldehydes. The synthetic scope for chiral α-heteroatom substituted aldehydes is examined including their applications in synthesis.

Mechanistic Studies on the Organocatalytic α-Chlorination of Aldehydes: The Role and Nature of Off-Cycle Intermediates

Herein we report the isolation and characterization of aminal intermediates in the organocatalytic α-chlorination of aldehydes. These species are stable covalent ternary adducts of the substrate, the catalyst and the chlorinating reagent. NMR-assisted kinetic studies and isotopic labeling experiments with the isolated intermediate did not support its involvement in downstream stereoselective processes as proposed by Blackmond. By tuning the reactivity of the chlorinating reagent, we were able to suppress the accumulation of rate-limiting off-cycle intermediates. As a result, an efficient and highly enantioselective catalytic system with a broad functional group tolerance was developed.

Total Synthesis of ent-Ascospiroketal B

Ascospiroketal B was isolated from a marine-derived fungus as a structurally unique polyketide possessing a rare tricyclic core including 5,5-spiroketal-γ-lactone. An asymmetric total synthesis of ent-ascospiroketal B was achieved using an original synthetic route. The synthesis included the stereoselective construction of 5,5-spiroketal for ascospiroketal B and stereocontrolled construction of a quaternary asymmetric carbon by rearrangement of a trisubstituted epoxide.

Marine natural products

Covering: 2015. Previous review: Nat. Prod. Rep., 2016, 33, 382-431This review covers the literature published in 2015 for marine natural products (MNPs), with 1220 citations (792 for the period January to December 2015) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1340 in 429 papers for 2015), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Asymmetric Total Syntheses of ent-Ascospiroketals A and B

A new hypothetic biosynthesis of the tricyclic spiroketal core of ascospiroketals A and B is proposed, which guided the development of a novel synthetic strategy for the asymmetric total synthesis of ent-ascospiroketals A and B. The synthesis features an efficient ring contraction rearrangement of the 10-membered lactone to the tricyclic spiroketal cis-fused γ-lactone core, which served as the common intermediate for the synthesis of both ent-ascospiroketals A and B through the Stille coupling reaction at the final step. In addition, seven diastereomers were prepared to conclusively confirm the structure of ent-ascospiroketal B.