Tolyporphins A–R, unusual tetrapyrrole macrocycles in a cyanobacterium from Micronesia, assessed quantitatively from the culture HT-58-2

Abstract

The ‘pigments of life’ family has been enlarged by the discovery of the tetrapyrrole macrocycles dubbed tolyporphins, which are present in a cyanobacterial culture (HT-58-2). Of the 18 known tolyporphins, fourteen (A–J and L–O) are dioxobacteriochlorins, three (K, Q and R) are oxochlorins, and one (P) is a porphyrin. The members with a given chromophore absorb similarly but not identically with each other, presenting the problem of absorption spectral aliasing. Tolyporphins G and H are isomers, as are tolyporphins L–O, given the nature of the peripheral (C-glycoside, –OH, or –OAc) substituents, presenting the (isobaric) problem of mass spectrometric analysis. The distribution of tolyporphin members is known to change over time and under different growth conditions, yet the complexity of the tolyporphins mixture presents challenges toward characterization of the underlying factors that alter such distributions. Liquid chromatography-mass spectrometry with dynamic multiple reaction monitoring (LC-MS-dMRM) was employed to characterize the distribution of tolyporphins under distinct growth media, using two semisynthetic standards, tolyporphin A O,O-dibutyrate and tolyporphin D O,O,O,O-tetrabutyrate. Growth in media containing both ammonium and nitrate salts versus nitrate alone affords increased production of tolyporphins. The absorption spectra of tolyporphins A–R have been reevaluated with regards to molar absorption coefficients, are compared with those of selected tetrapyrrole macrocycles to better understand the effects of chromophores and substituents, and are made available here in print and digital forms for comparison with isolated tolyporphins and mixtures thereof. Together, the work provides the foundation for quantitative assessment of these unusual natural products.