A New Hydroxy-acid in the Peel of Apple Fruits

DURING the examination of paper chromatograms of extracts from whole mature Edward VII apples, a faint acid spot appeared which did not correspond in position with any of the usual fruit acids. On chromatograms of extracts of peel tissue only, the unknown acid appeared to be present in an amount approximately one-quarter that of the malic acid present (the chief acid present in the fruit). About half a gram of the unknown acid was isolated in the pure form from peel tissue extracts by means of silica gel chromatography 1 , avoiding contact of the extracts with strongly basic ion-exchange resins during the process 2 . The acid crystallized with difficulty from water as needle-like crystals. Recrystallized from ether it gave a melting point of 94–96° C. On elementary analysis the acid proved to have a molecular formula corresponding to C 5 H 8 O 5 (C = 41.5, H = 5.4 per cent); its silver salt had a silver content of 58.5 per cent. The molecular weight (Rast) was found to be 146. The acid gave on analysis 9 per cent ‘OH’; the hydroxyglutaric acids contain 11.5 per cent ‘OH’, but β-hydroxy-acids tend to lose water when treated with acetic anhydride, which would lead to low results in the determination of ‘OH’ groups. Solutions of the acid gave a positive Denigès test 3 after oxidation with potassium permanganate. These facts provide the basis for its provisional identification as either β-OH-glutaric acid or citramalic acid. Further details will be published elsewhere.