They have either an
aldehydefunctional group in position 1 (aldoheptoses) or a
ketone functional group in position 2, 3 or 4 (ketoheptoses). Ketoheptoses have 4 chiral centers, whereas aldoheptoses have 5.
Examples
There are few examples of seven-carbon sugars in nature, among which are:
L-glycero-D-manno-heptose (an aldose), a late intermediate in lipid A biosynthesis.[4]
References
^Horecker, B. L; Smyrniotis, P. Z (1953). "Transaldolase: The Formation of Fructose-6-Phosphate from Sedoheptulose-7-Phosphate". Journal of the American Chemical Society. 75 (8): 2021.
doi:
10.1021/ja01104a532.