Reduction of Chlorophyllides, Chlorophylls and Chlorophyll Derivatives by Sodium Borohydride.

Sodium borohydride is a well known reducing agent. In methanol at room temperature formyl and keto groups are readily reduced to alcohol groups, while ester and carboxyl groups, carbon-carbon and carbon-nitrogen double bonds are only reduced with difficulty (2, 17). Of the groups present in chlorophyll b the C3 formyl and the C9 keto groups should be amenable to reduction, while the C2 vinyl and the C7 and Ci0 ester groups should be unaffected. Similar considerations apply to chlorophyll a and other derivatives containing formyl and keto groups. Since previous methods of reducing pheophorbides a and b had caused either reduction of the C2 vinyl group (6, 8) or had proceeded poorly (10), it was of interest to investigate the action of sodium borohydride upon these compounds and their magnesium salts (phyllins). Furthermore, there remained the possibility that reduction of the C9 keto group might involve formation of an intermediate similar to the pink product of the "Krasnovsky reaction" (the reversible photobleaching of chlorophyll a by ascorbic acid in pyridine) (23). This communication dlescribes the preparation and the properties of the products obtainecl by treating methyl chlorophyllides a and b and other chlorophyll derivatives with sodium borohydride. HCl numbers, wave lengths and relative absorbancies of visible absorption maxima and minima, useful for identification purposes, are included.