Department of Biochemistry, College of Medicine, University of Vermont, Burlington, Vermont, USA.
Department of Chemistry, University of Vermont, Burlington, Vermont, USA.
J Pept Sci. 2021 Oct;27(10):e3339. doi: 10.1002/psc.3339. Epub 2021 May 18.
Ergothioneine (EGT) is the betaine of 2-thiohistidine (2-thioHis) and may be the last undiscovered vitamin. EGT cannot be incorporated into a peptide because the α-nitrogen is trimethylated, although this would be advantageous as an EGT-like moiety in a peptide would impart unique antioxidant and metal chelation properties. The amino acid 2-thioHis is an analogue of EGT and can be incorporated into a peptide, although there is only one reported occurrence of this in the literature. A likely reason is the harsh conditions reported for protection of the thione, with similarly harsh conditions used in order to achieve deprotection after synthesis. Here, we report a novel strategy for the incorporation of 2-thioHis into peptides in which we decided to leave the thione unprotected. This decision was based upon the reported low reactivity of EGT with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), a very electrophilic disulfide. This strategy was successful, and we report here the synthesis of 2-thioHis analogues of carnosine (βAH), GHK-tripeptide, and HGPLGPL. Each of these peptides contain a histidine (His) residue and possesses biological activity. Our results show that substitution of His with 2-thioHis imparts strong antioxidant, radical scavenging, and copper binding properties to the peptide. Notably, we found that the 2-thioHis analogue of GHK-tripeptide was able to completely quench the hydroxyl and ABTS radicals in our assays, and its antioxidant capacity was significantly greater than would be expected based on the antioxidant capacity of free 2-thioHis. Our work makes possible greater future use of 2-thioHis in peptides.
ergothioneine (EGT) 是 2-硫代组氨酸（2-thioHis）的甜菜碱，可能是最后一种未被发现的维生素。由于α-氮被三甲基化，EGT 不能掺入到肽中，尽管作为肽中的 EGT 类似物，它会赋予独特的抗氧化和金属螯合特性。氨基酸 2-硫代组氨酸是 EGT 的类似物，可以掺入到肽中，尽管文献中仅报道了一次这种情况。一个可能的原因是保护硫酮所需的苛刻条件，合成后实现去保护也需要类似苛刻的条件。在这里，我们报告了一种将 2-硫代组氨酸掺入肽中的新策略，我们决定不保护硫酮。这一决定是基于 EGT 与 5,5'-二硫代双（2-硝基苯甲酸）（DTNB）的低反应性，DTNB 是一种非常亲电的二硫键。该策略取得了成功，我们在这里报告了肌肽（βAH）、GHK 三肽和 HGPLGPL 的 2-硫代组氨酸类似物的合成。这些肽都含有组氨酸（His）残基，并具有生物活性。我们的结果表明，用 2-硫代组氨酸取代 His 会赋予肽强烈的抗氧化、清除自由基和结合铜的特性。值得注意的是，我们发现 GHK 三肽的 2-硫代组氨酸类似物能够完全淬灭我们测定中的羟基和 ABTS 自由基，其抗氧化能力明显大于游离 2-硫代组氨酸的抗氧化能力。我们的工作使未来在肽中更广泛地使用 2-硫代组氨酸成为可能。
