[D-Ala2]deltorphin II is a highly stable amphibian heptapeptide and one of the most potent and selective δ-opioid receptor agonists known, with higher affinity and selectivity for δ-opioid receptors than any endogenous mammalian opioid ligand. It exhibits favorable enzymatic stability in brain membrane homogenates and plasma, with its blood-brain barrier (BBB) permeability influenced by its N-terminal region and residues at positions 4 and 5.

In mice, intracerebroventricular administration of [D-Ala2]deltorphin II produces significant antinociceptive effects, and repeated exposure leads to marked homologous tolerance without cross-tolerance to the δ₁ agonist DPDPE or the μ agonist DAMGO, indicating distinct receptor regulatory mechanisms.

It acts as a selective δ₂-opioid receptor agonist, whose antinociceptive signaling is coupled to Gq proteins and involves inositol-signaling pathways, distinguishing it from δ₁ agonists such as DPDPE, which rely on Go1 proteins.

• Thomas SA, Abbruscato TJ, Hau VS, et al. Structure-activity relationships of a series of [D-Ala2]deltorphin I and II analogues; in vitro blood-brain barrier permeability and stability. J Pharmacol Exp Ther. 1997;281(2):817-825.
• Mattia A, Vanderah T, Mosberg HI, Porreca F. Lack of antinociceptive cross-tolerance between [D-Pen2, D-Pen5]enkephalin and [D-Ala2]deltorphin II in mice: evidence for delta receptor subtypes. J Pharmacol Exp Ther. 1991 Aug;258(2):583-7. PMID: 1650835.
• Sánchez-Blázquez P, Garzón J. delta Opioid receptor subtypes activate inositol-signaling pathways in the production of antinociception. J Pharmacol Exp Ther. 1998 May;285(2):820-7. PMID: 9580632.

三氟乙酸（Trifluoroacetic acid，简称 TFA）是高效液相色谱（简称 HPLC）纯化过程中常用的反离子。TFA 的存在可能会对肽的净重量、外观及溶解度产生影响，具体如下：

对净重量的影响：TFA 盐会增加产物的总质量。在大多数情况下，肽的含量占总重量的 80% 以上，剩余部分则为 TFA。

对溶解度的影响：TFA 盐通常能提高肽在水溶液中的溶解度。

在生物检测中的影响：对于大多数标准的体外检测，残留的 TFA 水平一般不会造成干扰。但需注意，在高灵敏度的细胞研究或生化研究中，需关注其存在可能带来的影响。

干品多肽的重量中不仅仅包含多肽，还包含有一些非肽的组份，如水、被吸收的溶剂、配位离子和盐等。肽的净含量是指肽在其中的重量百分比，这个百分比的数值范围很大，可能从50%到90%，取决于纯度、序列以及合成和纯化的方法，不要将肽的净含量和肽的纯度混为一谈，他们是两个完全不同的概念。纯度通常是通过HPLC测定的。纯度定义的是多肽样品中含正确序列的组分的百分比，而肽的净含量是指样品中肽类物质相对于总物质所占的百分比，肽的净含量通常是氨基酸组分分析或紫外分光法测定的，这个信息主要是在一些对肽的浓度很敏感的实验中，对计算肽的浓度是很重要的。