The main nonpolar chlorophyll c from Emiliania huxleyi (Prymnesiophyceae) is a chlorophyll c(2)-monogalactosyldiacylglyceride ester: a mass spectrometry study

The main nonpolar chlorophyll c-like pigment was extracted from Emiliania h uxleyi (Lohm.) Hay et Mohler (strain CCMP 370) cultures and isolated by pre parative column chromatography and HPLC. The pigment, whose visible spectru m closely resembled that of chlorophyll ca, was studied by low-resolution f ast atom bombardment mass spectrometry, showing a very high mass molecular ion (m/z 1313). The fragment ions, either in the direct spectrum or obtaine d by tandem mass spectrometry with collision-induced dissociation of the mo lecular ion, were compatible with the consecutive losses of two fatty acids (14:0 and 18:4), glycerol, and a hexose, leaving a chlorophyll c(2) backbo ne, suggesting the molecule consists of a chlorophyll c(2) residue linked, via an ester bond, to the sugar moiety of a monohexosyldiacylglycerol. The identities of the two fatty acid residues (14:0 and 18:4n-3) were subsequen tly corroborated by gas chromatography of the corresponding methyl esters. Chemical hydrolysis-derivatization-gas chromatography-mass spectrometry dem onstrated the occurrence of glycerol and that galactose is the constituent sugar. The porphyrin obtained on acid hydrolysis showed chromatographic and visible spectral properties identical to pheoporphyrin Cp. This evidence l ed us to propose a tentative structure whose molecular formula, C76H96O14N4 Mg, was supported by the values of exact mass measurements by high-resoluti on fast atom bombardment mass spectrometry. This novel structure represents the highest molecular weight natural chlorophyll described to date.