Identification of Novel Low-Weight Sulfhydryl Conjugates of Oxidized 5- O- and 6- O-Substituted Betanidin Pigments

Agnieszka Kumorkiewicz-Jamro; L Ukasz Popenda; Sl Awomir Wybraniec

doi:10.1021/acsomega.0c00378

Identification of Novel Low-Weight Sulfhydryl Conjugates of Oxidized 5- O- and 6- O-Substituted Betanidin Pigments

ACS Omega. 2020 Jun 16;5(25):14955-14967. doi: 10.1021/acsomega.0c00378. eCollection 2020 Jun 30.

Authors

Agnieszka Kumorkiewicz-Jamro¹, L Ukasz Popenda², Sl Awomir Wybraniec¹

Affiliations

¹ Department of Analytical Chemistry, Institute C-1, Faculty of Chemical Engineering and Technology, Cracow University of Technology, ul. Warszawska 24, Cracow 31-155, Poland.
² NanoBioMedical Centre, Adam Mickiewicz University in Poznań, Wszechnicy Piastowskiej 3, 61-614 Poznań, Poland.

Abstract

The formation of conjugates of oxidized betacyanin pigments with selected low-weight sulfhydryl scavengers was studied. Short-lived quinonoids, quinone methides, and aminochromes derived from oxidized betacyanins are able to form adducts with different efficiencies. In this report, mass spectrometric and NMR identifications of CS-linked conjugates of cysteine, cysteamine, N-acetylcysteine, and dl-dithiolthreitol with quinonoid forms generated through oxidation of betanidin, betanin, and gomphrenin is presented. An adduct that formed between cysteine and quinonoid generated from betanin by its oxidation and decarboxylation (2-decarboxy-xanbetanin) was detected and reported for the first time. The most stable gomphrenin CS-conjugate, N-acetylcysteinylated gomphrenin, was isolated by semipreparative chromatography and its structure was established by NMR analysis. This enabled to confirm the conjugation position at carbon C-4 and to indicate the presence of a dopachromic intermediate during oxidation of gomphrenin. Conjugation of betacyanins with thiol-bearing moieties may generate new molecules with modified chemical and biological properties. Obtained results confirm that gomphrenin is capable of forming CS-conjugates with higher efficiency than betanin.