丁糖（Tetrose）是含有四个碳的单糖，分为丁醛糖和丁酮糖两类。

D-赤藓酮糖是唯一存在于自然界的丁酮糖。

果聚糖： 菊粉 · 果聚糖β2→6

甘露聚糖

半乳聚糖

A tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde functional group in position 1 (aldotetroses) or a ketone functional group in position 2 (ketotetroses).

D-Erythrose

D-Threose

D-Erythrulose

The aldotetroses have two chiral centers ("asymmetric carbon atoms") and so 4 different stereoisomers are possible. There are two naturally occurring stereoisomers, the enantiomers of erythrose and threose having the D configuration but not the L enantiomers. The ketotetroses have one chiral center and, therefore, two possible stereoisomers: erythrulose (L- and D-form). Again, only the D enantiomer is naturally occurring.