Two New Malyngamides from a Madagascan Lyngbya majuscula

Abstract

The lipid extract of a Madagascan Lyngbya majuscula has yielded malyngamides Q and R, both amides of 7-methoxytetradec-4-enoic acid. The isolation of these metabolites was accomplished using preparative liquid chromatography, with final purification through repetitive reversed-phase HPLC. Structure elucidation was accomplished utilizing 1D and 2D NMR spectroscopic characterization of the natural products and comparisons with malyngamides A and B. DPFGSE 1D NOE data suggested a different geometrical stereochemistry at C-6 in malyngamides Q and R from that observed for malyngamide A, as well as the other known malyngamides. The Z stereochemistry was confirmed for malyngamide R by measurement of key diagnostic (3)J(CH) couplings utilizing the HSQMBC pulse sequence. The absolute stereochemistry of C-4' ' of the pyrrolidone ring was defined by chiral GCMS analysis of serine released by ozonolysis and acid hydrolysis.

Analyses, extensions and comparison of three experimental schemes for measuring (nJCH+DCH)-couplings at natural abundance

“…Especially 3 J CH coupling constants follow the Karplus relation and build a more reliable tool for the determination of relative configurations as e.g. NOE connectivities, which often do not allow unambiguous conclusions [1][2][3][4][5][6][7][8][9][10][11][12].…”

Determination of the stereochemistry of γ‐Butyrolactones by DPFGSE‐NOE experiments

“…The introduced DPFGSE-NOE method provides spectra without subtraction artifacts and thus allows the observation of NOE enhancements of as little as 0.02%. Milligan et al 17 used the DPFGSE-NOE spectra to determine the absolute configuration of olefins in some lipid extracts, which are secondary metabolites of the marine cyanobacterium Lyngbya majuscula; Liptaj et al 18 proved the DPFGSE-NOE experiment to be very useful for the observation of long-range NOE between the two xanthene units of biosynthesized neosatorin; Bauer et al 19 showed the advantage of DPFGSE-ROE in their study on calixarene derivatives, which are molecules of medium size. In this paper, we describe the elucidation of the conformation of compounds 1-4 using DPFGSE-NOE spectra.…”

Various Entries to Vinyl Chloride Derivatives and their Applications in Total Synthesis of Natural Products

“…Spongistatin-1, 4 a famous natural product endowed with a nanomolar level of cytotoxicity, bears such a function too. Other examples include: welwistatin (3), 5 pinnaic acid (4), 6 malyngamide Q (5), 7 and penasin B (6), 8 but this list is not exhaustive. There are also pharmaceuticals that contain a vinyl chloride function, such as clomiphene (7), an anti-estrogen drug.…”