D-threose

Threose is a four-carbon monosaccharide with molecular formula C4H8O4. It has a terminal aldehyde group, rather than a ketone, in its linear chain and so is considered part of the aldose family of monosaccharides. The threose name can be used to refer to both the - and -stereoisomers and more generally to the racemic mixture (/L-, equal parts D- and L-) as well as to the more generic threose structure (absolute stereochemistry unspecified).

The prefix "threo-" which derives from threose (and "erythro-" from a corresponding diastereomer erythrose) offer a useful way to describe general organic structures with adjacent chiral centers, where "the prefixes... designate the relative configuration of the centers". As is depicted in a Fischer projection of -threose, the adjacent substituents will have a syn orientation in the isomer referred to as "threo", and are anti in the isomer referred to as "erythro".