Oxygen family important reactions

The formation of C-alkaloid D from C-dihydrotoxiferine I by aerial oxidation in dilute aqueous mineral acid has already been mentioned. This is one of several important reactions which show that many of the calabash curare and Strychnos alkaloids can be grouped together in so-called families containing mutually related alkaloids. Thus, C-dihydrotoxiferine I is converted into C-curarine by irradiation of the solid alkaloid in the presence of oxygen (110) similar irradiation of a solution of the alkaloid in the presence of eosin gives C-calebassine (110). C-Calebassine is also formed from C-dihydrotoxiferine I by the action of hot acetic acid in pyridine in the presence of oxygen (111). The production of C-fluorocurarine from C-calebassine and from C-curarine has already been noted. These reactions are summarized in Scheme 2. 

Carbonates represent an important family of protecting groups of hydroxyl groups. All of the members of the carbonate family are easy to introduce by reaction of the free alcohol with chloroformates or mixed carbonate esters. In general, carbonates are less reactive than esters towards basic hydrolysis owing to the reduced electrophilicity of the carbonyl afforded by the resonance deactivation by two oxygens. However, the conditions that attack esters may also attack carbonates. 

In those organisms that perform photosynthesis, further phosphorylation of D-ribulose 5-phos-phate into D-ribulose 1,5-diphosphate by phosphoribulokinase represents an important prerequisite in CO2 fixation. As has already been mentioned, the key and extensively studied enzyme involved in this reaction is D-ribulose 1,5-bisphosphate carboxylase/oxygenase. The subfamily divergence in this multigene family has been studied in certain plants of Triticeae and other families [13]. The occurrence of this enzyme in anoxic Archaea is very interesting, since it had to evolve in the absence of molecular oxygen [14]. 

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