Enantioselective Total Synthesis of (−)‐Candelalides A,B and C: Potential Kv1.3 Blocking Immunosuppressive Agents

Potential immunosuppressive agents : Candelalides A, B and C (see figure), novel blockers of the voltage‐gated potassium channel Kv1.3, have been efficiently synthesized for the first time in a convergent and unified manner starting from (+)‐5‐methyl‐Wieland–Miescher ketone. The method explored has potential for preparing various types of candelalide analogues for the structure–activity relationship studies.

     

Total Synthesis of (−)‐Amphidinolide K

Macrolide magic : An enyne cross‐metathesis reaction of an alkynyl boronate with an alkene derivative as well as a radical cyclization reaction of a homopropargylic β‐alkoxyacrylate are the key transformations in the total synthesis of the cytotoxic macrolide (?)‐amphidinolide K.

     

Concise Total Synthesis of Nannocystin A

Nannocystin A, a structurally unique 21‐membered macrocyclic depsipeptide with low nanomolar inhibitory activity against elongation factor 1A, was synthesized according to a strategy involving the vinylogous Mukaiyama aldol reaction, Sharpless epoxidation, olefin metathesis, the Mitsunobu reaction, and a palladium‐catalyzed intramolecular Suzuki coupling of a highly complex cyclization substrate. The overall synthesis is efficient and paves the way for preparation of analogues for drug development efforts.     

Total Syntheses of Amphidinolides B1, B4, G1, H1 and Structure Revision of Amphidinolide H2

Nature is a pretty unselective “chemist” when it comes to making the highly cytotoxic amphidinolide macrolides of the B/G/H series. To date, 16 different such compounds have been isolated, all of which could now be approached by a highly convergent and largely catalysis‐based route (see figure). This notion is exemplified by the total synthesis of five prototype members of this family.

     

Total Synthesis of Berkelic Acid

A productive total synthesis of both enantiomers of berkelic acid ( 1 ) is outlined that takes the structure revision of this bioactive fungal metabolite previously proposed by our group into account. The successful route relies on a fully optimized triple‐deprotection/1,4‐addition/spiroacetalization cascade reaction sequence, which delivers the tetracyclic core 32 of the target as a single isomer in excellent yield. The required cyclization precursor 31 is assembled from the polysubstituted benzaldehyde derivative 20 and methyl ketone 25 by an aldol condensation, in which the acetyl residue in 20 transforms from a passive protecting group into an active participant. Access to fragment 25 takes advantage of the Collum–Godenschwager variant of the ester enolate Claisen rearrangement, which clearly surpasses the classical Ireland–Claisen procedure in terms of diastereoselectivity. Although it is possible to elaborate 32 into the target without any additional manipulations of protecting groups, a short detour consisting in the conversion of the phenolic ? OH into the corresponding TBS‐ether is beneficial. It tempers the sensitivity of the compound toward oxidation and hence improves the efficiency and reliability of the final stages. Orthogonal ester groups for the benzoate and the aliphatic carboxylate terminus of the side chain secure an efficient liberation of free berkelic acid in the final step of the route.     

Phormidolides B and C,Cytotoxic Agents from the Sea: Enantioselective Synthesis of the Macrocyclic Core

New cytotoxic polyketide macrolides named phormidolides B and C were isolated from a marine sponge of the Petrosiidae family collected off the coast of Pemba (Tanzania). The isolation, structure elucidation, and enantioselective synthesis of three diastereomers of the macrocyclic core is described herein. The described synthetic methodology started from 2‐deoxy‐D ‐ribose or 2‐deoxy‐L ‐ribose and afforded the desired macrocycles with high enantiomeric purity. The key step of the synthesis is the formation of the Z‐trisubstituted double bond using a Julia–Kocienski olefination. The versatility of the synthetic methodology may provide access to other enantiopure macrocycles by making changes in the starting materials or chiral inductors.     

Total Synthesis and Bioactivity Mapping of Geodiamolide H

The first total synthesis of the actin-stabilizing marine natural product geodiamolide H was achieved. Solid-phase based peptide assembly paired with scalable stereoselective syntheses of polyketide building blocks and an optimized esterification set the stage for investigating the key ring-closing metathesis. Geodiamolide H and synthetic analogues were characterized for their toxicity and for antiproliferative effects in cellulo, by characterising actin polymerization induction in vitro, and by docking on the F-actin target and property computation in silico, for a better understanding of structure-activity relationships (SAR). A non-natural analogue of geodiamolide H was discovered to be most potent in the series, suggesting significant potential for tool compound design.     

A Formal Total Synthesis of Taxol Aided by an Automated Synthesizer

A 36‐step synthesis was carried out in automated synthesizers to provide a synthetic key intermediate of taxol. A key step involved a microwave‐assisted alkylation reaction to construct the ABC ring system from an AC precursor. Subsequent formation of the D ring afforded baccatin III, a well‐known precursor of taxol.