For ANTIMICROBIAL COMPOUNDS OF THE MARINE RED ALGA MARGINISPORUM ABERRANS: The fresh alga (15 kg) was washed with water, air-dried and extracted with MeOH. The extract showed marked antimicrobial activity against Bacillus subtilis. After removing the solvent, the residue was separated into n-hexane- and Et₂O-soluble neutral, EtOAc-soluble acidic and Et₂O-soluble basic fractions. Si gel chromatography of the Et₂O-soluble neutral fraction (n-hexane-EtOAc, 3:1) gave an active compound (8 mg), mp 113-114°C which was found to be identical with p-hydroxybenzaldehyde by comparison (mmp, IR, NMR, MS) with authentic sample. Recently, Fenical and McConnell [1] also isolated p-hydroxybenzaldehyde as an antimicrobial component of the red alga Dasya pedicellata var. stanfordiana. Continued elution gave dichloroacetamide (15 mg), mp 98-99°C which was identical in all respects (IR, NMR, MS) to an authentic sample. In 1967, Khaskin and coworkers [2] synthesized a variety of amides and measured their antimicrobial activities, and they found dichloroacetamide showing moderate activity against Botorytis cinerea and Alternaria radicina. Si gel chromatography of the EtOAc-soluble acidic fraction using CHCl₃-EtOAc (5:1) and crystallization from n-hexane-Et₂O afforded 3,5-dinitroguaiacol (10 mg, mp 124-125°C; νmax cm⁻¹: 3500, 1625, 1570, 1550 and 1355; λmax nm (log ε): 213(4.33), 266(3.98), 332(3.81) and 410(3.04); ¹H NMR (100 MHz): 4.06(3H, s), 8.02(1H, d, J=3Hz), 8.74(1H, d, J=3Hz) and 11.22(1H, s). Direct comparison (mmp, IR, NMR) with an authentic sample confirmed the identity. 3,5-Dinitroguaiacol showed marked antimicrobial activity against B. subtilis. This is the first report of the isolation of dichloroacetamide and 3,5-dinitroguaiacol as natural products. For QUINONES FROM PEREZIA RUNCINATA: The hexane extract of 24 g of the roots of Perezia runcinata yielded 600 mg of a red oil which by PMR analysis showed the presence of perezone type signals, in addition to other peaks. The oil was separated by chromatography into perezone isovalerate (or O-isovalerylperezone) and the two hydroxyperezone monoisovalerates which were identified spectroscopically and by hydrolysis which gave the respective parent quinones and isovaleric acid. Definitive proof of the structure of isovalerylperezone (1b) was obtained by alkaline hydrolysis which afforded perezone (1a) identified by standard procedures with an authentic sample [1] and isovaleric acid, characterized by its PMR spectrum and comparison of the corresponding anilide derivative with a sample prepared specifically [2]. Chemical confirmation of the hydroxyperezone esters was also obtained by alkaline treatment, which yielded hydroxyperezone and isovaleric acid, characterized as the anilide [2]. Thus only the position of the ester has to be defined in order to establish the complete structures. In earlier work [3] we were able to define the esterifying position of a monoangeloyl hydroxyperezone by methylation of the free alcohol group, removal of the ester group and comparison of the product with a sample synthesized from perezone (1a). Therefore a portion of the red oil was esterified with Me₂SO₄ yielding a mixture of the two isomers 2b and 3b in almost equimolecular proportion, since in the PMR spectrum the hydroxyl signal originally at 7.04 ppm disappeared, two methoxyl singlets at 3.98 and at 4.02 ppm appeared and two quinonoid methyl signals at 1.88 and 1.93 ppm are now seen, instead of one signal at 1.91 ppm present before methylation. The structural assignment of 2b as the less polar constituent and of 3b as the more polar one was done after detailed PMR considerations. Comparison of the chemical shifts of the quinonoid methyl group in 3-hydroxythymoquinone [4] with its corresponding methyl ether and in 6-hydroxythymoquinone also with the derived ether, reveals that the chemical shift difference for the C-methyl group associated with the methoxylation process is greater in the 3-substituted compounds than in the 6-substituted series, since in the first case the O-methyl group is introduced adjacent to the existing quinonoid methyl group. Similar differences are observed upon comparison of the spectrum of the mixture 2a and 3a with the spectra of the O-methylated derivatives 2b and 3b. Furthermore, treatment of this derivative with Eu(DPM)₃ shift reagent, revealed that greater shifts are induced to both the C-methyl and O-methyl groups of 3b than to the same groups in 2b. This is in agreement with the structural assignment of the isomers, since on one hand there appears to be no association at the ester carbonyls, as deduced from the chemical shifts of the