Detection of Menaquinone-6 and a Novel Methyl-substituted Menaquinone-6 in Campylobacter jejuni and Campylobacter fetus subsp. fetus

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Abstract
Menaquinone-6 (2-methyl-3-farnesyl-farnesyl-1,4-naphthoquinone) and a methyl-substituted menaquinone-6 (2,[5 or 8]-dimethyl-3-farnesyl-farnesyl-1,4-naphthoquinone) were the major isoprenoid quinones found in membrane preparations of C. jejuni and C. fetus ssp. fetus. By reverse-phase high-performance liquid chromatography (HPLC) and TLC the faster-eluting menaquinone-6 co-chromatographed with a menaquinone-6 standard. The identity of menaquinone-6 was confirmed by UV spectrophotometry, mass spectrometry and NMR analysis. The slower-eluting methyl-substituted menaquinone-6 co-chromatographed with a menaquinone-7 standard by reverse-phase TLC but eluted between menaquinone-6 and menaquinone-7 standards by HPLC. The UV spectrum of the methyl-substituted menaquinone-6 did not correlate with either authentic menaquinone or demethylmenaquinone. Mass spectra showed an increase of 14 mass units when compared to menaquinone-6, and indicated that a methyl substitutent was on the naphthoquinone nucleus. NMR spectra confirmed the presence of a methyl substituent at a peri position (C-5 or -8) on the benzenoid ring.