Synthesis and Stereochemistry of the C30−C63 Section of Karlotoxin 2

Abstract

Karlotoxin 2 (KmTx2) is a marine natural product isolated from the dinoflagellate Karlodinium veneficum. The absolute configuration of KmTx2 was determined by NMR analysis in combination with degradation of the natural product, and the absolute configuration at C49 was revised by computational analysis. On the other hand, we reported revision of the absolute configuration of amphidinol 3 (AM3), whose structure is similar to that of KmTx2, by comparing NMR data of the synthesized partial structures and total synthesis of AM3. In this paper, we report the synthesis of the partial structures of KmTx2 corresponding to the C30À C63 section, and the diastereomer at C37, C41À C43, and C45À C49, which is hypothetically proposed on the basis of the revised structure of AM3. Comparison of the NMR data of the synthetic specimens with those of the natural product suggested that the absolute configuration of KmTx2 is revised to be 37R, 41R, 42R, 43R, 45R, 46R, 47R, 48S, and 49S.

Marine natural products

“…[348][349][350][351] The total synthesis of amphidinol-3 has been achieved, 352 as has that of karlotoxin-2 881, which necessitated its structural revision to that shown here. 353 Unexpected new bioactivities can be found for known compounds. The effects of brevetoxin-2 in reversing the effects of strokes in mice have been investigated.…”

“…The total synthesis of amphidinol-3 has been achieved, 352 as has that of karlotoxin-2 881 , which necessitated its structural revision to that shown here. 353…”

Synthesis of the MN Ring of Caribbean Ciguatoxin C-CTX-1 via Desymmetrization by Acetal Formation

“…Removal of the acetyl groups of 9 was carried out, giving hydroxy ketone 4 . We previously reported that removal of the acetyl groups proceeded effectively by using a solid catalyst under flow conditions . This procedure is useful for water-soluble polar products such as 4 , because enough pure material can be obtained after the concentration of the eluent without further purification.…”