No abstract

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. MATERIALS AND METHODSSolvents were reagent grade and were used without further purification. Sodium borohydride was obtained from Metal Hydrides Inc., Beverly, Mass. andl was about 99 % pure.Methyl chlorophyllides a and b, chlorophylls a and b. andl pheoporphyrin a5 and phylloerythrin were obtained pure by standard procedures (13,15,19,20,22,25). "Meso" derivatives were prepared bv catalytic hydrogenation of the parent compounds in acetone containing palladium black as the catalyst (14). Free acids were obtained by hydrolysis of the C7 ester in strong hydrochloric acid for 30 minutes at room temperature (12). For the phase test, 0.1 ml of methanolic magnesium methoxide (18 mg Mg/ml) was

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

Treatment of chlorophyll a or methyl chlorophyllide a with potassiun~ permanganate effected oxidation of the 2-vinyl group without concomitant oxidation of the cyclopentanone ring. One of the products obtained was of especial interest because its visible absorption spectrum was identical with that of a previously known, but chemically uncharacterized, pigment-chlorophyll d. The preparation and identification of this oxidation product as 2-desvinyl-2-formyl-chlorophyll-a is given and its probable identity with chlorophyll d is discussed in detail.Chlorophyll d is a pigment which has been reported to occur in a number of species of the Rhodophyceae, a group which contains chlorophyll a but, a t most, only traces of chlorophyll b (1, 2). I t was first isolated and described by Manning and Strain in 1943 (2). Recently Smith and Benitez (3) obtained chromatographically pure samples and calculated the specific absorption curve by determining the magnesium content and by assuming the molecular weight to be that of chlorophyll a (see Fig. 1). T o date its chemical constitution has not been determined nor has any useful function been ascribed to it, although there have been speculations that it may be responsible for the anomalous action spectra of photosynthesis and chlorophyll fluorescence in red algae (1).The present work arose from some observations made in connectioll with studies on the allomerizatio~l of chlorophyll a. When the phase test intermediate of chlorophyll a , in acetone containing base, was treated with dilute permanganate, it was oxidized immediately. Examination with a visual spectroscope showed a "red" absorption maximum a t about 675 mp, which was characteristic of Mg-purpurin-18 (4). However, when base was omitted a gradual but different spectral change occurred; two new "red" maxima appeared a t about 650 and 685 mp. When the mixture was chromatographed, there were, besides a minor zone of unchanged chlorophyll a , three new zones. The pigments were designated as fractions A, B, and C, in the relative order of their position .. .on the column, fraction C being uppermost. Each fraction gave a positive phase test which indicated that allomerizatioil had not occurred. Most interesting was fraction A which had visible absorption spectra in methanol and in ether which were identical with those published for chlorophyll d (2, 3). The present comm~nication describes fraction A and evidence to indicate that it is similar to and probably identical with chlorophyll d. Fractions B and C will be discussed in a subsequent commt~nication. The change in spectrum obtained when fraction A in isopropanol was treated with methanolic magnesium methoxide (4) is given in Fig. 2. Enhanced absorption in the 'illantiscript