An improved synthesis of (−)-brevisamide, a marine monocyclic ether amide of dinoflagellate origin

Stereoselective Synthesis of Allylic Alcohols via Substrate Control on Asymmetric Lithiation

Allylic alcohols are a privileged motif in natural product synthesis and new methods that access them in a stereoselective fashion are highly sought after. Toward this goal, we found that chiral acetonide-protected polyketide fragments performing the Hoppe-Matteson-Aggarwal rearrangement in the absence of sparteine with high yields and diastereoselectivities rendering this protocol a highly valuable alternative to the Nozaki-Hiyama-Takai-Kishi reaction. Various stereodyads and -triads were investigated to determine their substrate induction. The mostly strong inherent stereoinduction was attributed to a combination of steric and electronic effects.

Studies towards the Synthesis of (–)-Pulvomycin: Construction of the C12–C40 Segment by a Stereoselective Aldol Reaction

A convergent strategy was developed for the synthesis of the C12–C40 segment of (–)-pulvomycin. Key step was a diastereoselective aldol reaction between a chiral ethyl ketone representing the C24–C40 fragment and a chiral aldehyde representing the C12–C23 fragment. Both compounds were prepared from enantiomerically pure building blocks in a convergent fashion. The longest linear sequence commenced with a known d-fucose-derived glycosyl donor and entailed a total number of 16 steps. The desired anti-aldol product was obtained in a total yield of 5% over these steps and contains 12 out of 13 stereogenic centers present in the natural product.

Total Synthesis of Brevisamide Using an Oxiranyl Anion Strategy

A total synthesis of brevisamide, a marine monocyclic ether amide isolated from the dinoflagellate Karenia brevis, has been achieved in 18 steps starting from 4-(benzyloxy)butanol. The synthesis involves oxiranyl anion coupling between an epoxy sulfone and a triflate, intramolecular etherification of a hydroxy-bromoketone, diastereoselective introduction of the axial methyl group by hydroxyl-directed hydrogenation of an exocyclic olefin, and installation of an acetamide side chain by nucleophilic substitution of an N-acetyl carbamate. The dienal side chain is assembled using a Horner-Wadsworth-Emmons reaction to complete the synthesis.

A concise asymmetric total synthesis of (+)-brevisamide

A new protecting-group-free synthesis of the marine monocyclic ether (+)-brevisamide is reported. The enantioselective synthesis utilizes a key asymmetric Henry reaction and an Achmatowicz rearrangement for the formation of the tetrahydropyran ring. A penultimate Stille cross-coupling allows for an efficient installation of the conjugated (E,E)-diene side chain ultimately delivering (+)-brevisamide.

A Formal Total Synthesis of (-)-Brevisamide

A formal total synthesis of (-)-brevisamide has been achieved. The synthetic approach highlights a chemoselective asymmetric dihydroxylation and a one-pot Fraser-Reid epoxidation/PMB protection reaction sequence.

Total synthesis of (-)-brevisin: a concise synthesis of a new marine polycyclic ether

The first and highly efficient total synthesis of (-)-brevisin has been achieved. The title compound was synthesized in only 29 steps (longest linear sequence) from commercially available starting materials. The synthesis provided over 70 mg of a marine polycyclic ether compound.