The historically relevant D/L system relates chiral molecules to the D and L enantiomers of glyceraldehyde. The stereodescriptors D and L are accepted in CurlySMILES notations for molecules with one asymmetric atom:
load gif/DglyceraldehydeSketch.gif load gif/LglyceraldehydeSketch.gif
load gif/DglyceraldehydeFischer.gif load gif/LglyceraldehydeFischer.gif
D-glyceraldehyde L-glyceraldehyde
The systematic name of D-glyceraldehyde is (R)-2,3-dihydroxypropanal:
OCC{D}(O)C=O and OCC{R}(O)C=O encode the same enatiomer.

The systematic name of L-glyceraldehyde is (S)-2,3-dihydroxypropanal:
OCC{L}(O)C=O and OCC{S}(O)C=O encode the same enatiomer.

Another example is L-cysteine with the systematic name (R)-2-amino-3-sulfanylpropanoic acid:
O=C(O)C{L}(N)CS and O=C(O)C{R}(N)CS encode the same enatiomer.

Molecules with more than one stereogenic center should always be encoded by using the R and S stereodescriptors, illustrated for (2R,3R)-2,3,4-trihydroxybutanal, commonly known as D-erythrose:
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[1] B. Testa: Principles of organic stereochemistry.
Marcel Dekker, New York and Basel, 1979.
[2] D. Hellwinkel: Systematic Nomenclature of Organic Chemistry.
Springer-Verlag, Berlin und Heidelberg, Germany, 2001.
[3] A. Drefahl: CurlySMILES: a chemical language to customize and annotate encodings of molecular and nanodevice structures. J. Cheminf. 2011, 3:1; doi: 10.1186/1758-2946-3-1 .

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