Hisatoshi Uehara

Organocatalytic Enantioselective Synthesis of Nitrogen-Substituted Dihydropyran-2-ones, a Key Synthetic Intermediate of 1β-Methylcarbapenems

Organocatalytic enantioselective cycloadditions providing nitrogen-substituted dihydropyran-2-ones were developed in two catalytic systems. The (3R,4R)-product was a versatile intermediate in the synthesis of 1beta-methylcarbapenem antibiotics.

Convergent synthesis of the HIJKLM ring fragment of ciguatoxin CTX3C

Abstract Ciguatoxin CTX3C is a representative congener of the ciguatoxins, which are known to be the principal causative agents of ciguatera food poisoning. The structure of CTX3C spans more than 3xa0nm and is characterized by 13 ether rings. To attain a practical construction of this molecule, efficient supplies of the structural fragments are crucial. Herein we report the convergent synthesis of the HIJKLM ring fragment and present a new carbonyl olefination protocol to cyclize the J ring using low-valent titanium.

Convergent synthesis of the EFGH ring fragment of ciguatoxin CTX3C

Abstract A stereoselective synthesis of the EFGH ring fragment of ciguatoxin CTX3C has been achieved through: (i) selective cleavage of a dioxepane acetal Cue5f8O bond; (ii) radical cyclization to form the oxepane G ring; and (iii) chemoselective ring-closing metathesis of a triene yielding the hexahydrooxonin F ring.

A concise route to the right wing of ciguatoxin

A concise route to the HIJKLM-ring fragment 10 of ciguatoxin (CTX) and 51-hydroxyCTX3C was developed in which oxiranyl anion addition and intramolecular carbonyl olefination were utilized as key transformations. The present procedure requires only 23 steps from the I-ring 5, while 35 steps were employed in a previous synthesis of the corresponding right wing 11 of CTX3C. The high efficiency of the present synthesis ensures a supply of 10 for total synthesis and biomedical applications.

The absolute configuration and total synthesis of korormicin

The marine antibiotic korormicin, isolated from the culture filtrate of marine bacterial strain Pseudoalteromonas sp. F-420, specifically inhibits the growth of marine Gram-negative bacteria without affecting terrestrial species. The absolute configuration of korormicin was determined by the combination of a CD exciton chirality method and chemical degradation. Convergent total synthesis of koromicin has been also achieved.

Practical entry into the HIJKLM ring segment of ciguatoxin CTX3C

The HIJKLM ring segment (27) of the right half portion of nciguatoxin CTX3C (1) has been synthesized using a ring-closing reaction nmediated by a low-valent titanium reagent.

CONVERGENT SYNTHESIS OF THE IJKLM RING FRAGMENT OF CIGUATOXIN CTX3C

The IJKLM ring fragment of CTX3C, an important member of the ciguatoxin family, was synthesized via ring-closing metathesis using the Tebbe reagent and an improved method of reductive hydroxy ketone cyclization.