The monoacetate of O-methylasparvenone

New Bioactive Metabolites from a Freshwater Isolate of the Fungus Kirschsteiniothelia sp.

“…Component 4 (12.1 mg) was eluted as a white crystalline solid from CH2Cl2-Me2CO (3:1) and was found to be O-methylasparvenone, although it had an optical rotation opposite in sign to that of the 0methylasparvenone isomer reported in the literature. The [a}D value was determined to be -25.1°( c = 0.6, MeOH), as compared to the reported value of + 22°(r = 2.6, MeOH) for the literature compound (6). However, the absolute stereochemistry has not been determined.…”

“…This assignment was further supported by 1H-*H decoupling experiments which clearly showed sharpening of each individual MeO singlet upon irradiation of the neighboring (ortho) aromatic proton signal. 13C-nmr chemical shift assignments for 1 (6) and subunit a are in very close agreement, with each carbon shift in a differing by no more than 0.8 ppm from the corresponding value for 1. a b A major fragment ion at mlz 274.0476 in the hreims of 5 could not be attributed to subunit a, and must correspond to the remaining portion of 5, which has the formula Cl4H10O6. Ten of the carbons and two oxygens could be accounted for by a second naphthoquinone skeleton.…”

“…Component 7 (2.7 mg) eluted at CH2Cl2-Me2CO (2:3) as a yellow crystalline solid and was found to be 6-ethyl-7hydroxy-2-methoxyjuglone (10). 'H-nmr data for 7 have not been reported previously: (CDC13) 12.65 (1H, s), 7.09 (1H, s), 6.00 (1H, s), 3.87 (3H, s), 2.72 (2H, q,/=6), 1.16 (3H, t,/=6).…”

“…After 12 days, the EtOAc-Me2CO (9:1) extract of the culture filtrate was subjected to cc on Si gel to afford five major components. Four of these metabolites were identified as 6-ethyl-2,7-dimethoxyjuglone {1}, 6-( 1-hydroxyethyl)-2,7 -dimethoxyj uglone [2], a monoacetyl derivative of 2 [3], and (-)-0-methylasparvenone [4j. The structures of these compounds were established by comparison of their spectral properties (nmr, ms, ir, uv) to literature values for compounds 1 and 2 and the ( + )-enantiomer of 4, all of which had been previously reported (4)(5)(6).…”

“…Most of the known naphthoquinone dimers occur in a direct head-to-head or tailto-tail linkage. There are a few examples of symmetrical dimers linked by an ethylidene unit {e.g., ethylidene-6,6'-biplumbagin [6] from the fruit of Diospyros marítima ( 8)].…”