noun, plural: heptoses
Monosaccharides are the simplest form of carbohydrates. They are classified according to the number of carbon atoms in a monosaccharide. In particular, a heptose is a monosaccharide with seven carbon atoms. Monosaccharides may also be classified based on the type of carbonyl group they contain. An aldose is a monosaccharide that contains an aldehyde group (-CHO) at position 1 whereas a ketose is one that contains a ketone (C=O) at position 2. Thus, an aldoheptose is a heptose with an aldehyde group. A ketoheptose, in contrast, is a heptose with a ketone functional group located in position 2.
Aldoheptoses have five chiral centers. An example of a naturally-occurring aldoheptose is L-glycero-D-manno-heptose. It is a heptose with a chemical formula of C7H14O7. It is an intermediate in lipid A biosynthesis. It occurs in plants, e.g. carrots, apricots, and apples.
Ketoheptoses have four chiral centers. An example of a naturally-occurring ketoheptose is sedoheptulose. It has a chemical formula of C7H14O7. It is an early intermediate in lipid A biosynthesis. It is found in alfalfa, avocado, and fig. Another example of a ketoheptose is mannoheptulose. It is a heptose found in avocados.
Word origin: hept(a)- ("seven") + -ose (relating to sugars)