An Assessment of the Rubisco Inhibitor: 2-Carboxyarabinitol-1-Phosphate and d-Hamamelonic Acid 2-Phosphate Are Identical Compounds

2-Carboxyarabinitol-1-phosphate, the nocturnal inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase is identical with d-hamamelonic acid-2¹-phosphate. Reasoning is based on theoretical considerations as well as on mass spectra and ¹H- and ¹³C-NMR spectra of the phosphate-free compounds. d-Hamamelonic acid-2¹-phosphate is interpreted as a metabolic derivative of d-hamamelose-2¹,5-bisphosphate which originates in the chloroplast from fructose-1,6-bisphosphate. A simple method for the synthesis of the inhibitor is suggested.