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The new α-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. &gt; 2.5 × 10 -5  м . Its chemical structure was elucidated by mass spectrometry,  1 H-and  13 C-NMR spectroscopy to be 3-methyl-1-oxa-bicyclo (4,1,0) hept-5-en-2-one-4,6-dicarboxylic acid di­methylester (II). It is derived from 3-methyl-2H-pyran-2-one-4,6-dicarboxylic acid by cyclo-propanation 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 NMR spectroscopy. I shows less inhibition of seed germination than II. The reference a-pyrones dimethyl-6-methyl-2H-pyran-2-one-3,5-dicarboxylate (III) , 3-methoxycarbonyl-5-methoxycar-bonylmethyl-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.

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