Malyngamides M and N from the Hawaiian Red Alga Gracilaria coronopifolia

Abstract

Two new malyngamides, M and N (1, 2), were isolated along with malyngamide I acetate (3) from the Hawaiian red alga Gracilaria coronopifolia. Our results suggest that malyngamide N (2) is a revised structure of deacetoxystylocheilamide (5). The absolute configuration of malyngamide I acetate was deduced to be 3 using the reversed octant rule.

Total synthesis of malyngamide M and isomalyngamide M

“…(1) were identical with those of the natural product. 6 While comparing the NMR data of Z-1 with those of isolated malyngamide M, the obvious differences of chemical shift were observed in the vicinity of the vinyl chloride functionality, such as H-1 0 , H-3 0 , H-NCH 3 , C-1 0 , C-3 0 and C-1 00 position. The maximum discrepancy of chemical shift was 0.23 ppm for 1 H NMR at H-1 0 position, and 2.9 ppm for 13 C NMR at C-1 0 and C-1 00 positions.…”

“…It should be noted that, some of the 1 H NMR signals of synthetic 1 and Z-1 appeared as pairs of peaks due to the presence of two tert-amide isomers, but 13 C NMR signals did not appear as pairs of peaks, but this is a fairly common phenomenon observed among the malyngamides. 1a, 6,18 The benzophenone-sensitized photochemical Z-E isomerization reaction of vinyl chloride was also applied to other substrates. In the above conditions, compound 9 and 10 were both decomposed maybe due to the existence of the MOM group in their skeletons.…”

“…Malyngamide M (1) was isolated from the Hawaiian red alga Gracilaria coronopifolia by Nagai's group. 6 It was the first example of a natural aromatized malyngamide, which possesses a special terminal vinyl chloride substructure. The compound also shows weak cytotoxicity to NB cells (IC 50 >20 mM).…”

Toxins Associated With Medicinal and Edible Seaweeds

“…Nagai et al soon identified aplysiatoxin (19) and debromoaplysiatoxin (20) as the major causative agents of the Hawaiian Gracilaria poisonings (57). They subsequently reported additional related compounds, manauealides A-C (21)(22)(23), and malyngamides M (24) and N (25) from the samples of the alga collected at the same site of the original toxic specimen (58,59). Manauealides induced diarrhea in mice similar to aplysiatoxin and debromoaplysiatoxin (58), Toxin Reviews Downloaded from informahealthcare.com by UB Frankfurt/Main on 09/01/14…”

“…while the malyngamides exhibited weak cytotoxicity against mouse neuroblastoma (NB) cells in culture (59). Aplysiatoxins were first reported as the toxins of the sea hare Stylocheilus longicauda (60) and subsequently as the constituents of the blue-green alga Lyngbya majuscula (61), a diet of the sea hare.…”