Hamamelonic acid

The carbon-chain structure of the sugar obtained from hamameli-tannin was established by the classical method of Kiliani,26 which is based on the reduction, with hydrogen iodide, of polyhydroxy acids to fatty acids. Treatment of the calcium salt of hamamelonic acid under these conditions led to inconclusive results. The reduction of the corresponding, crystalline ammonium salt, however, furnished 3.5 to 5% of 2-methylvaleric acid, which was identified by the properties of its crystalline p-iodophenacyl ester. Thus, it was proved that the sugar must have structure XIV. 

The extension of the salt-acid,27 phenylhydrazide,28 and amide rules29 to the derivatives of the 2-(hydroxymethyl) sugars by Schmidt and Weber-Molster30 indicated that the configuration of C2 in hamamelonic acid is the same as that of D-ribonic acid. Finally, the d-ribo configuration of the sugar was established by the synthesis of hamamelonic acid and its C2 epimer from D-ery/ftro-pentulose31 by the cyanohydrin reaction of Fischer and Kiliani. 

Rubisco Rubisco might be primarily responsible for limiting COp-fixation under certain conditions (22). However, the very complex mooes of regulation of this key enzyme of COp-fixation still remain to be elucidated. Particularly the eventually light-dependent metabolism (23) of the recently discovered inhibitor carboxyarabinitol-l-P (24) (which is identical with hamamelonic acid-2 -phosphate (25)) might be a crucial site of regulation which is not yet understood at all. 

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