小分子(英语:small molecule)是一个有机化学概念。一般将分子量小于900道尔顿的有机化合物分子称为小分子[1]。小分子的直径以纳米计。目前大部分药物都是小分子类药物,蛋白质、核酸等生物大分子的基本组成单位(如氨基酸、核糖核苷酸、脱氧核苷酸)也是小分子。
小分子药物一般是抑制剂,通过干扰蛋白间相互作用起效[2]。
目前大部分的药物都是小分子药物[3]
。小分子的分子量上限一般设在900道尔顿。这是因为900道尔顿以下的分子在人体内能较快速地扩散进入细胞,到达作用靶点[1][4]。根据里宾斯基五规则,口服给药的小分子药物的分子量最好能低于500道尔顿,否则损耗率会出现明显上升[5][6]。
Macielag MJ. Chemical properties of antibacterials and their uniqueness. Dougherty TJ, Pucci MJ (编). Antibiotic Discovery and Development. 2012: 801–2 [2020-01-16]. ISBN 978-1-4614-1400-1. (原始内容存档于2020-08-18). The majority of [oral] drugs from the general reference set have molecular weights below 550. In contrast the molecular-weight distribution of oral antibacterial agents is bimodal: 340–450 Da but with another group in the 700–900 molecular weight range.
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