Total Synthesis of Loroxanthin

Abstract

The first total synthesis of loroxanthin (1) was accomplished by Horner-Wadsworth-Emmons reaction of C25-apocarotenal 8 having a silyl-protected 19-hydroxy moiety with C15-phosphonate 25 bearing a silyl-protected 3-hydroxy-ε-end group. Preparation of apocarotenal 8 was achieved via Stille coupling reaction of alkenyl iodide 10 with alkenyl stananne 9, whereas phosphonate 25 was prepared through treatment of ally alcohol 23 with triethyl phosphite and ZnI2. The ally alcohol 23 was derived from the known (3R,6R)-3-hydroxy C15-aldehyde 20, which was obtained by direct optical resolution of racemate 20 using a semi-preparative chiral HPLC column.

Marine natural products

“…338,339 Only one rst total synthesis of a brown algal MNP was reported in 2022, that of carotenoid loroxanthin. 340 Reviews focusing on brown algae and their metabolites published in 2022 include summaries of the anticancer activity of various eckols and fucoxanthin, respectively, 341,342 phlorotannins as sedative aids for promoting sleep, 343 and catalogues of the compounds found from species Ecklonia stolonifera, 344 and the genera Dictyota and Dictyopteris, respectively. 345,346 An in silico study of various brown algal phlorotannins as SARS-COV-2 protease inhibitors identied several lead compounds, which were then validated as weak to moderate inhibitors using in vitro bioassays.…”