Phloroglucinol compounds of natural origin

This review describes the various manifestations of the pyrimidine system (alkylated, glycosylated, benzo-annelated.). These comprise pyrimidine nucleosides as well as alkaloids and antibiotics – some of them have been discovered and isolated from natural sources already long time ago, others have been reported very recently. A short overview on pyrimidine syntheses (prebiotic synthesis, biosynthesis, and metabolism) is given. The biological activities of most of the pyrimidine analogs are briefly described, and, in some cases, syntheses are formulated.

Pyrimidine as constituent of natural biologically active compounds.

Occurrence and distribution of free flavonoid aglycones in plants

Isoprenylated flavonoids—a survey

A strategy to achieve ortho substitution of phenols initiated by an ortho-palladation to create coumarins was examined Indeed, treatment of alkynoates with electron-rich phenols in the presence of a palladium catalyst and an acid does generate coumarins The scope of the reaction with respect to the phenol and the alkynoates is defined With unsymmetrical aromatic substrates, generally good regioselectivity that reflects the HOMO coefficients can be observed In the course of these studies, numerous important naturally occurring coumarins have been synthesized, including fraxinol methyl ether, ayapin, herniarin, xanthoxyletin, and alloxanthoxyletin The fact that a Pd(0) is the precatalyst rather than a Pd(+2) species and that an acid that reduces Pd(+2) salts, formic acid, functions better than other carboxylic acids raises doubts about the initial working hypothesis A novel mechanism involving a palladium phenoxide formed from a hydridopalladium carboxylate and phenol is invoked to rationalize the results

David L. Dreyer

Papers

Distribution of limonoids in the rutaceae

Alkaloids of some Mexican Zanthoxylum species

Extractives of Geijera parviflora

Alkaloids, limonoids and furocoumarins from three Mexican Esenbeckia species

Coumarins of Citrus macroptera