Alkyl sulfur chlorophyll derivatives: Preparation and liquid chromatography-multistage tandem mass spectrometric characterisation of analogues of naturally occurring sedimentary species

A series of synthetic sulfur-containing chlorophyll derivatives with alkyl sulfur groups attached to the C-31 position, the same as in structures proposed for natural alkyl sulfur chlorophyll derivatives, has been prepared from the chlorophyll a derivative, methyl pyrophaeophorbide a. The synthetic compounds exhibit shifts in high performance liquid chromatography (HPLC) retention times and online UV/vis absorption maxima relative to methyl pyrophaeophorbide a, consistent with those observed between the natural alkyl sulfur chlorophyll derivatives and their non-sulfurised counterparts. The 1H nuclear magnetic resonance and multistage tandem mass spectra of the synthetic and natural alkyl sulfur chlorophyll derivatives show close agreement. The prominent loss of the C-31 alkylsulfur group as a radical during multistage tandem MS has been confirmed as a diagnostic feature of the compounds.