[Borek]

Landis is a cyclist who won this year's Tour de France but was later found cheating with testosterone. I have just found an interesting post at sci.chem, by Eric Lucas:

First line screening looks for an epimer of natural testosterone, not an enantiomer--an epimer has one isomerized chiral center, as opposed to being entirely of the opposite handedness.  Since the synthetic stuff is almost certainly made by elaborating some other readily-available naturally occurring steroid, most of the chiral scaffolding of the molecule is already fixed, with only one or two chiral centers introduced in the synthesis. After a positive first-line screen, the second-line screen is based on the C-13 content.  My understanding is that the unusual epi-testosterone ratio can (not likely, but can) occur due to abnormal but natural metabolic processes, but an unusual C-13 content is unequivocally from man-made material.

[Borek]

Ahh, sometimes there is nothing like browsing blogs:

testosterone_carbon_isotopes_and_floyd_landis