Docosahexaenoic acid in regio- and enantiopure triacylglycerols : Oxidative stability and influence of chiral antioxidant

Funding Information: The authors would like to thank Dr. Jukka-Pekka Suomela for the guidance of using UHPLC -QTOF and Linda Intonen for assistance with part of the practical work related to fatty acid analysis. Personal financial grant to Annelie Damerau from the Finnish Cultural Foundation is acknowledged. Further, personal financial grants to Eija Ahonen from Niemi Foundation, the Finnish Cultural Foundation and the Finnish Food Research Foundation are acknowledged. This work entity was carried out as part of the Academy of Finland funded project “Omics of oxidation – Solutions for better quality of docosahexaenoic and eicosapentaenoic acids” (grant number 315274, PI Kaisa M. Linderborg). Publisher Copyright: © 2022 The Author(s)Docosahexaenoic acid (DHA) is essential for health but easily oxidized. Yet the influence of DHA's exact location (sn-1, sn-2, or sn-3) in triacylglycerols on oxidative stability is currently unknown. This is the first study comparing oxidative stability of DHA in regio- and enantiopure triacylglycerols with or without RRR-α-tocopherol. Headspace solid-phase micro-extraction with gas chromatography–mass spectrometry, liquid chromatography–mass spectrometry, and nuclear magnetic resonance spectroscopy were applied. DHA in sn-2 was the most stable with or without added RRR-α-tocopherol resulting in differences in hydroperoxide formation. Without antioxidant, stability of DHA in sn-1 and sn-3 was mainly similar, with slight tendency towards better stability in sn-3. With RRR-α-tocopherol higher stability in sn-1 compared to sn-3 was observed. This points to diastereomeric interactions between RRR-α-tocopherol and DHA in sn-1. These results are highly relevant for enzymatic restructuring processes of DHA-rich fish or microalgae oil concentrates aimed for food supplements or food fortification.Peer reviewe

Synthesis of the C1-C27 fragment of stambomycin D validates modular polyketide synthase-based stereochemical assignments

The stambomycins are a family of bioactive macrolides isolated from Streptomyces ambofaciens. Aside from two stereocenters installed through cytochrome P450 oxidations, their stereochemistry has been predicted by sequence analysis of the polyketide synthase. We report a synthesis of the C1-C27 fragment of stambomycin D, the spectroscopic data of which correlates well with that of the natural product, further validating predictive sequence analysis as a powerful tool for stereochemical assignment of complex polyketide natural products

Synthesis of the C50 diastereomers of the C33–C51 fragment of stambomycin D

As products of genome mining, the stereochemical assignment of the macrolide antibiotics stambomycins A–D has been made on the basis of sequence analysis of the associated polyketide synthase, aside from two stereocentres at C28 and C50. Here we describe syntheses of the two C50 diastereomers of the C33–C51 region of the stambomycins, which support the PKS-based configurational assignment, and establish a strategy suitable for access to the extended stambomycin framework