Natural Inhibitors of Germination and Growth, III New a-Pyrones from Seeds of Rosa canina

The new a-pyrone derivative II was isolated in crystalline form from extracts of dormant seeds of Rosa canina. It inhibits germination of seeds of Amaranthus caudatus completely, but reversibly, at conc. > 2.5 x 10~5 m . Its chemical structure was elucidated by mass spectrometry, 'Hand 13CNMR spectroscopy to be 3-methyl-l-oxa-bicyclo (4,1,0) hept-5-en-2-one-4,6-dicarboxylic acid di­ methylester (II). It is derived from 3-methyl-2H-pyran-2-one-4,6-dicarboxylic acid by cyclopropanation with diazomethane. The parent compound which is a natural product of the seeds of Rosa canina was isolated as its dimethyl ester I the structure of which was elucidated by mass and NM R spectroscopy. I shows less inhibition of seed germination than II. The reference a-pyrones dimethyl-6-methyl-2H-pyran-2-one-3,5-dicarboxylate ( II I) , 3-methoxycarbonyl-5-methoxycarbonylmethyl-6-methyl-2H-pyran-2-one (IV), and isodehydracetic acid methylester (V) did not show any inhibitory activity. The relationship of II with threo-dihydrohematinic acid (VII) is discussed.