Modular total syntheses of the marine-derived resorcylic Acid lactones cochliomycins a and B using a late-stage nozaki-hiyama-kishi macrocyclization reaction

Total Syntheses of Strasseriolide A and B, Antimalarial Macrolide Natural Products

We report the first total syntheses of strasseriolide A and B. Strasseriolide B shows potent activity against the wild-type malaria parasite Plasmodium falciparum and good activity against a chloroquine-resistant strain. A convergent strategy was envisioned with an aldehyde-acid fragment and a vinyl iodide-alcohol fragment. Both fragments were prepared using chiral pool starting materials. They were combined with a Yamaguchi esterification and cyclized with a Nozaki-Hiyama-Kishi reaction. Strasseriolide B was assembled in a 16-step LLS.

Total Synthesis of Cladosins B and C

A convergent synthetic route to the fungal metabolites cladosins B and C has been developed, affording these natural products in 29% and 27% overall yield, respectively. The cladosins are rare examples of hybrid polyketides featuring a 3-enamine tetramic acid group derived from l-valine. Key steps in this modular six-step sequence include a DMAP-mediated O- to C-acyl rearrangement to unite the side chains with the tetramic acid core and subsequent amine incorporation using either ammonium acetate or HMDS.

Asymmetric total synthesis of filamentous fungi related resorcylic acid lactones 7-epi-zeaenol and zeaenol

An efficient, short and, a convenient asymmetric total synthesis of filamentous fungi related resorcylic acid lactones 7-epi-zeaenol (2) and zeaenol (1) have been achieved in 7 and 9 linear steps with the high overall yield of 32% and 21% respectively, from the known intermediate 13. Mitsunobu inversion, De Brabander’s protocol for macrolactonisation, Heck cross-coupling, diastereoselective alkyne aldehyde coupling and Ohira–Bestmann alkynylation are the key reactions.

Asymmetric total synthesis of paecilomycin C through intramolecular nucleophilic ring opening of an epoxide

An efficient asymmetric total synthesis of naturally occurring resorcylic acid lactone (RAL) paecilomycin C was achieved by employing carboxylate assisted 5-exo-tet ring opening of an epoxide as a key reaction.

Stereoconfining macrocyclizations in the total synthesis of natural products

This review covers selected examples of point chirality-forming macrocyclizations in natural product total synthesis in the past three decades.

Gold-Catalyzed Oxidative Coupling of Alkynes toward the Synthesis of Cyclic Conjugated Diynes

A gold-catalyzed oxidative coupling of alkynes was developed as an efficient approach for the synthesis of challenging cyclic conjugated diynes (CCD). Compared to the classical copper-promoted oxidative coupling reaction of alkynes, this gold-catalyzed process exhibits a faster reaction rate due to the rapid reductive elimination from the Au(III) intermediate. This unique reactivity thus allowed a challenging diyne macrocyclization to take place in high efficiency. Condition screening revealed a [(n-Bu)₄N]⁺[Cl-Au-Cl]^- salt as the optimal pre-catalyst. Macrocycles with ring size between 13 to 28 atoms were prepared in moderate to good yields, which highlighted the broad substrate scope of this new strategy. Furthermore, the synthetic utilities of the cyclic conjugated diynes for copper-free click chemistry have been demonstrated, which showcased the potential application of this strategy in biological systems.

Scalable Regioselective and Stereoselective Synthesis of Functionalized (E)-4-Iodobut-3-en-1-ols: Gram-Scale Total Synthesis of Fungal Decanolides and Derivatives

A reliable protocol to synthesize both racemic and chiral (E)-4-iodobut-3-en-1-ols from aldehydes or epoxides, respectively, containing various aromatic and aliphatic substitutions has been established. The utility of these compounds was then demonstrated by providing access to known fungal decanolides as well as novel aromatic macrocycles. The protocol provided a gram-scale route to (-)-aspinolide A and (-)-5-epi-aspinolide A utilizing a catalytic Nozaki-Hiyama-Kishi reaction to close the macrolide in the final step in 65-84% yields.

Resorcylic acid lactones (RALs) and their structural congeners: recent advances in their biosynthesis, chemical synthesis and biology

Resorcylic acid lactones (RALs) are naturally occurring 14-membered macrolactones that constitute a class of polyketides derived from fungal metabolites and that possess significant and promising biological activity.

Discovery, Semisynthesis, Antiparasitic and Cytotoxic Evaluation of 14-Membered Resorcylic Acid Lactones and Their Derivatives

Ten antifouling 14-membered resorcylic acid lactones 1-10 were isolated previously with low or trace natural abundance from the zoanthid-derived Cochliobolus lunatus fungus. Further optimization of fermentation conditions led to the isolation of two major natural compounds 7 and 8 with multi-gram quantities. By one or two steps, we semisynthesized the six trace natural compounds 1-6 and a series of derivatives 11-27 of compounds 7 and 8 with high yields (65-95%). Compounds 11-13 showed strong antiplasmodial activity against Plasmodium falciparum with IC50 values of 1.84, 8.36, and 6.95 μM, respectively. Very importantly, 11 and 12 were non-toxic with very safety and high therapeutic indices (CC50/IC50 > 180), and thus representing potential promising leads for antiplasmodial drug discovery. Furthermore, 11 was the only compound showed obvious antileishmanial activity against Leishmania donovani with an IC50 value of 9.22 μM. Compounds 11 and 12 showed the values of IC50 at 11.9 and 17.2 μM against neglected Chagas' disease causing Trypanosoma cruzi, respectively.

Total Syntheses of the Resorcylic Acid Lactones Paecilomycin F and Cochliomycin C Using an Intramolecular Loh-Type α-Allylation Reaction for Macrolide Formation

Subjection of the resorcylic ester 16 to a Nozaki-Hiyama-Kishi reaction afforded the 12-membered lactone 17, while treatment of it under the Loh-type α-allylation conditions using indium metal gave the isomeric, 14-membered macrolide 18. Compound 18 was readily elaborated to the resorcylic acid lactone type natural products paecilomycin F and cochliomycin C.

Concise synthesis of calystegines B2 and B3via intramolecular Nozaki-Hiyama-Kishi reaction

The key step in the concise syntheses of calystegine B2 and its C-2 epimer calystegine B3 was the construction of cycloheptanone 8via an intramolecular Nozaki-Hiyama-Kishi (NHK) reaction of 9, an aldehyde containing a Z-vinyl iodide. Vinyl iodide 9 was obtained by the Stork olefination of aldehyde 10, derived from carbohydrate starting materials. Calystegines B2 (3) and B3 (4) were synthesized from d-xylose and l-arabinose derivatives respectively in 11 steps in excellent overall yields (27% and 19%).

Synthesis of the 2-formylpyrrole spiroketal pollenopyrroside A and structural elucidation of xylapyrroside A, shensongine A and capparisine B

A convergent synthesis enabled structural elucidation of the 2-formyl pyrrole spiroketals pollenopyrroside A and shensongine A/xylapyrroside A. The key step involves a Maillard-type condensation to furnish the 2-formylpyrrole ring system.

Total syntheses of the resorcylic acid lactone neocosmosin A and its enantiomer

A total synthesis of the structure, 1, assigned to the recently reported resorcylic acid lactone (RAL) neocosmosin A has been established. Olefin-cross metathesis, ring-closing metathesis, palladium-catalyzed Meinwald rearrangement, and Mitsunobu esterification reactions were used as key steps. A late-stage and simple modification to the reaction sequence also provided compound ent-1 that, in fact, represents the true structure of the natural product.