定义Definition
D/L 构型是以甘油醛为参照、在费歇尔投影式中比较手性碳（糖类为离羰基最远的手性碳，氨基酸为 α-碳）上 –OH 或 –NH₂ 位置的标记法：在右边为 D，在左边为 L。
The D/L system labels configuration relative to glyceraldehyde: in the Fischer projection, if the –OH (sugars, at the stereocentre farthest from the carbonyl) or –NH₂ (amino acids, at the α-carbon) is on the right it is D, on the left L.
糖与氨基酸Sugars and amino acids
天然糖多为 D 型（D-葡萄糖、D-核糖），天然蛋白质氨基酸为 L 型。L-氨基酸大多是 S 构型，但 L-半胱氨酸是 R（因为 S 原子使 CIP 优先次序改变）。
Natural sugars are mostly D (D-glucose, D-ribose) and protein amino acids L. Most L-amino acids are S, but L-cysteine is R because sulfur changes the CIP priorities.
由来Origin
费歇尔在 1891 年前后为糖类建立相对构型体系；罗萨诺夫（1906）建议统一以甘油醛为参照。
Fischer built the relative-configuration system for sugars around 1891; Rosanoff (1906) proposed glyceraldehyde as the universal reference.
与 d/l、R/S 区别Not d/l or R/S
小写 d/l（或 +/−）表示旋光方向，大写 D/L 表示构型，二者无必然关系：D-果糖是左旋的。现代命名通用 R/S，D/L 仍在生物化学中广泛使用。
Lowercase d/l (or +/−) denote rotation, capital D/L configuration; they are independent — D-fructose is laevorotatory. R/S is standard today, but D/L remains common in biochemistry.
年表Timeline
- 1891
费歇尔确定葡萄糖构型
Fischer determines the configuration of glucose
- 1906
罗萨诺夫提出以甘油醛为参照
Rosanoff proposes the glyceraldehyde reference