Total Synthesis and Structural Elucidation of Two Unusual Non‐Methylene‐Interrupted Fatty Acids in Ovaries of the Limpet Cellana toreuma

Abstract

In our previous study, unusual odd-numbered dienoic acids with a terminal olefin were found as minor components in ovaries of the Japanese limpet Cellana toreuma, and the synthetic interests have been focused onto their structural confirmation and the inspection into their potential biological activity. Here, we describe an efficient and stereoselective total synthesis of two new unusual dienoic acids, 19:2∆7,18 and 21:2∆7,20, through a common pathway involving the strategic combination of alkyne-zipper reaction and Lindlar hydrogenation for the construction of their unique carbon chains. In our synthetic study, 2-propyn-1-ol was at first subjected to alkylation and alkyne-zipper reaction to form the two fragments, and the subsequent carbon chain elongation was achieved by the usual coupling reaction to obtain the C-19 and C-21 products bearing an internal acetylenic group. Then, the internal acetylenic group of these products was subjected to Lindlar hydrogenation to form a Z-alkenyl moiety, and the subsequent deprotection of the products was carried out under an acidic condition without isomerization of the internal Z-alkenyl group. Total synthesis of target fatty acids, 19:2∆7,18 and 21:2∆7,20, was finally accomplished by two-step oxidation of the resulting alcohols into carboxylic acids in a highly chemoselective manner, and the structures of these unusual natural fatty acids were finally elucidated by identifying the GC-MS spectra of the methyl esters of authentic and synthetic fatty acids.

Diverse Odd‐Chain Monoenoic Fatty Acids and Novel Non‐Methylene‐Interrupted Heptadecadienoic Acids in Ovaries of the Limpet Cellana toreuma

“…). Interestingly, this finding shows that 17:2Δ5,16 and 17:2Δ7,16 are structural analogs of 19:2Δ7,18 and 19:2Δ9,18, respectively (Kawashima and Ohnishi, ; Shimada et al, ). Analog19:2Δ9,18 is observed as an analog of 21:2Δ11,20 (Kawashima and Ohnishi, ).…”

High-value compounds from the molluscs of marine and estuarine ecosystems as prospective functional food ingredients: An overview

“…The unreported odd-chain fatty acids were identified from the ovaries of Cellana toreuma , and their structures were confirmed by synthesis ( Shimada, Sugawara, Korenaga, & Kawashima, 2017 ). The Australian samples of Scutus antipodes afforded scutinin A 173 and scutinin B as epimers 174 – 175 with antibacterial and antifungal properties ( Chand & Karuso, 2017 ).…”

Marine natural products

“…Four new odd-chain fatty acids 1390-1393 were isolated from the ovaries of the limpet Cellana toreuma, 617 with the structures of 1390 and 1392 being conrmed by synthesis. 618 Australian samples of the keyhole or slit limpet Scutus antipodes afforded scutinin A 1394 a hexaester of D-sorbitol, and scutinin B as a 3 : 2 mixture of epimers 1395 and 1396. 619 The structures of scutinins A and B were conrmed by synthesis and antibacterial and antifungal activities reported.…”