It is been more than 20 years since l heard about L-Sugar. If l remember correctly, it is the mirror image of the sugar molecule. You can do everything with this sugar that you can with table sugar, but the body can not metabolize it. It is safe for diabetics and wo not cause tooth decay.

Why is not it on the market?

If my inductive and deductive reasoning skills are functioning properly, it is on the market in the form of ''tagatose''. Check it out:
http://wired.com/wired/archive/11.11/newsugar_pr.html

''Levin is long, strange search for the ultimate sugar replacement started three decades ago, when he stumbled upon chiral chemistry, the well-established principle that complex molecules exist in ''right-handed'' and ''left-handed'' forms, known as enantiomers''