Lipoic acid occurs in two forms which are enantiomers ("mirror images") of each other.

One form, R-lipoic acid is biologically active because it is a cofactor for some enzymes. The other enantiomer, S-lipoic acid, is biologically inactive.

[Edited]
Sorry, I used a different nomenclature to yours. In mine "R" is the same as "D" in yours (did you mean to type "D" rather than "R"?) and "S" is the same as "L" in yours.

So, what you want is R-lipoic acid (D-lipoic acid in your system) not S-lipoic acid (L-lipoic acid in your system).