A silver(I) complex of acetylsinigrin: Structure and myrosinase-like activity

• Main Authors: Alba, Laurenzo De Vera, Hatanaka, Tsubasa, Franco, Francisco C., Jr., Nojiri, Masaki, Noel, Marissa G., Funahashi, Yasuhiro
• Format: text
• Published: Animo Repository 2021
• Subjects: Glucosinolates; Chemistry
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/11274
• Institution: De La Salle University

Background: In plants, glucosinolates such as sinigrin are decomposed into glucose and the aglycone by the enzyme myrosinase through cleavage of the glycosidic C-S bond. The aglycone can rearrange to the corresponding isothiocyanate which has a defensive function. The inorganic method historically used to cleave the C-S bond is through Ag(I), but the mechanism remains unknown. Methods: Acetylation of sinigrin yielded O-acetylsinigrin, which was then treated with Ag(I) triflate to yield the Ag(I) complex (Ag·SinAc) which was characterized by X-ray crystallography. The Ag(I)- induced cleavage of the glycosidic C-S bond was evaluated by 1 H NMR spectroscopy in both sinigrin and O-acetylsinigrin. Density functional theory (DFT) and natural bonding orbital (NBO) analyses were used to determine the mechanism of the C-S bond activation in putative solution-state structures. Results: The crystal structure of Ag·SinAc was successfully refined showing that the Ag(I) ion is bound to acetylsinigrin though the sulfated thiohydroximate and to its ethylene moiety by an organometallic Ag-(η2-C=C) bond. The presence of Ag(I) ions readily cleaves the C-S bond of sinigrin at room temperature. The same reaction requires heating in the case of Ag·SinAc. The Ag(I)-induced reaction is analogous to the action of myrosinase. Theoretical calculations show that the C-S bond activation is largely due to the polarizing effect of Ag(I) coordination to the S atom, and the stabilization of the leaving group. Conclusions: An unprecedented Ag(I) complex of a glucosinolate derivative has been synthesized and structurally characterized, which allowed the mechanistic elucidation of the myrosinase-like activity of the Ag(I) ion.