Department of Biotechnology, Chemistry and Pharmacy, University of Siena, Via Aldo Moro, 2, 53100, Siena, Italy.
Dipartimento di Biotecnologie Mediche, University of Siena, Viale Bracci 16, 53100, Siena, Italy.
Mol Divers. 2023 Jun;27(3):1489-1499. doi: 10.1007/s11030-022-10505-6. Epub 2022 Aug 29.
Trifluoroacetic acid (TFA), due to its strong acidity and low boiling point, is extensively used in protecting groups-based synthetic strategies. Indeed, synthetic compounds bearing basic functions, such as amines or guanidines (commonly found in peptido or peptidomimetic derivatives), developed in the frame of drug discovery programmes, are often isolated as trifluoroacetate (TF-Acetate) salts and their biological activity is assessed as such in in vitro, ex vivo, or in vivo experiments. However, the presence of residual amounts of TFA was reported to potentially affect the accuracy and reproducibility of a broad range of cellular assays (e. g. antimicrobial susceptibility testing, and cytotoxicity assays) limiting the further development of these derivatives. Furthermore, the impact of the counterion on biological activity, including TF-Acetate, is still controversial. Herein, we present a focused case study aiming to evaluate the activity of an antibacterial AlkylGuanidino Urea (AGU) compound obtained as TF-Acetate (1a) and hydrochloride (1b) salt forms to highlight the role of counterions in affecting the biological activity. We also prepared and tested the corresponding free base (1c). The exchange of the counterions applied to polyguanidino compounds represents an unexplored and challenging field, which required significant efforts for the successful optimization of reliable methods of preparation, also reported in this work. In the end, the biological evaluation revealed a quite similar biological profile for the salt derivatives 1a and 1b and a lower potency was found for the free base 1c.
三氟乙酸（TFA）由于其强酸性和低沸点，广泛应用于基于保护基团的合成策略中。实际上，在药物发现计划框架内开发的具有碱性官能团（如胺或胍基（通常存在于肽或拟肽衍生物中））的合成化合物通常作为三氟乙酸盐（TF-Acetate）盐分离出来，并以这种形式评估其在体外、离体或体内实验中的生物活性。然而，据报道，残留的 TFA 含量可能会影响广泛的细胞测定的准确性和重现性（例如抗菌药敏试验和细胞毒性测定），从而限制了这些衍生物的进一步发展。此外，关于抗衡离子对生物活性的影响，包括 TF-Acetate，仍然存在争议。在此，我们进行了一项重点案例研究，旨在评估作为三氟乙酸盐（1a）和盐酸盐（1b）盐形式获得的具有抗菌作用的烷基胍基脲（AGU）化合物的活性，以强调抗衡离子在影响生物活性方面的作用。我们还制备并测试了相应的游离碱（1c）。应用于聚胍基化合物的抗衡离子交换代表了一个尚未开发的具有挑战性的领域，这需要付出巨大的努力来成功优化可靠的制备方法，本工作也对此进行了报道。最终，生物学评价显示盐衍生物 1a 和 1b 的生物学特征相当相似，而游离碱 1c 的活性较低。
