Search

The AlCl3-promoted reaction of methyl 2,5-dimethylpyrrole-1-carboxylate 1with dimethyl acetylenedicarboxylate affords under certain conditions a low yield of 2,5-dimethyl-2-tricarbomethoxyvinyl-2H-pyrrole 3. The structure of the latter was established on the basis of detailed 1H and 13C nmr studies, and confirmed by conversion to dimethyl 5-methyl-5-(3-oxobutyl)-3-pyrrolin-2-one-3,4-dicarboxylate 4.

Physciosporin, a new chlorinated depsidone, has been isolated from the lichen Pseudocyphellaria physciosporaand identified as methyl 2-chloro-4-formyl-3,8-dihydroxy-1,6,9-trimethyl-11-oxo-11H-dibenzo[b,e][1,4]dioxepin-7-carboxylate (methyl 5-chlorovirensate), 1.

Examination by 13C nuclear magnetic resonance spectroscopy of chartreusin produced in cultures of Streptomyceschartreusissupplemented with [1-13C] and [2-13C]acetate showed that the 19-carbon aglycone component was derived entirely from acetate. In the spectrum of chartreusin enriched from [1,2-13C]acetate the signals for 16 of the carbon atoms were accompanied by satellites due to spin–spin coupling of intact 13C—13C units. The coupled pairs were matched with the aid of homonuclear single 13C-frequency decoupling. Of the uncoupled carbon atoms, two were derived from methyl groups of acetate and the third came from an acetate carboxyl group. The arrangement of paired and unpaired 13C atoms in chartreusin suggests that the aglycone is derived from a single 22-carbon polyketide chain. Cyclization to a benzpyrene-like intermediate followed by ring cleavage and loss of three carbon atoms provides a plausible route from the polyketide to the substituted isocoumarin structure of the aglycone.

Direct irradiation (2537 Å) of methyl 1,4-diphenyl-1,4-epoxy-1,4-dihydronaphthalene-2-carboxylate (13b) affords methyl 2,4-diphenyl-3-benzoxepine-1-carboxylate (17b) and methyl 1-benzoyl-3-phenylindene-2-carboxylate (19b), while acetone-sensitized irradiation yields chiefly 19b. The latter can be converted to methyl 3-phenylindene-2-carboxylate (21b).Direct irradiation of dimethyl 1,4-diphenyl-1,4-epoxy-1,4-dihydronaphthalene-2,3-dicarboxylate (13a) affords a mixture of dimethyl 2,4-diphenyl-3-benzoxepine-1,5-dicarboxylate (17a), dimethyl 1-benzoyl-3-phenylindene-1,2-dicarboxylate (19a), and dimethyl 1-benzoyl-2-phenylindene-1,3-dicarboxylate (18). The latter two products cleave readily to give dimethyl 3-phenylindene-1,2-dicarboxylate (21a) and dimethyl 2-phenylindene-1,3-dicarboxylate (20) respectively. Sensitized irradiation yields mainly 19a. The formation of 19aand 19bas major products of photorearrangement of 13a and 13bis consistent with a di-π-methane pathway producing methyl 4,6-diphenyl-5-oxatetracyclo[5.4.0.0.2,403,6]undeca-1(7),8,10-triene 2-carboxylate and 2,3-dicarboxylate (25a,b), intermediates similar to those previously observed by other workers for benzonorbornadienes and 7-azabenzonorbornadienes. Compound 18is derived by photo-induced rearrangement of the benzoxepine 17a.The AlCl3-catalyzed rearrangement of 13ayields a mixture of dimethyl 2,4-diphenyl-1(2H)-naphthalenone-2,3-dicarboxylate (15) and methyl 1,3-diphenyl-4-hydroxynaphthalene-2-carboxylate (16), while that of 13baffords only 16.

The causative agent of toxicity in cultured mussels from a localized area of eastern Prince Edward Island has been identified as domoic acid, a neuroexcitatory amino acid. The toxin was isolated by a number of different bioassay-directed separation techniques including high-performance liquid chromatography, high-voltage paper electrophoresis, and ion-exchange chromatography, and characterized by a number of spectroscopic techniques including ultraviolet, infrared, mass spectrometry, and nuclear magnetic resonance. The isolation and purification methods are described in detail and some new analytical data for domoic acid are reported. Keywords: shellfish toxin, domoic acid, neurotoxin, bioassay-directed analysis.

The free radical addition of iodine to dimethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate (3a)yields three stereoisomeric dimethyl 3,5-diiodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes 4–6), as well as dimethyl 5,6-diiodobicyclo[2.2.1]hept-2-ene-2,3-dicarboxylate (9). By-products are two dimethyl 3-hydroxy-5-iodotricyclo[2.2.1.02,6]heptane-2,3-dicarboxylates (nortricyclenes 7, 8). Compounds 4and 5are also obtained as major products of addition of iodine to dimethyl tetracyclo[2.2.1.02,603,5]heptane-2,3-dicarboxylate (quadricyclane 10a). The structures of these various products were elucidated with the aid of 1H and 13C nmr and high-resolution mass spectroscopy.