Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential

Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P · Drug Testing and Analysis

The active ingredient of the TB-500 product analysed was the N-terminally acetylated seven-amino-acid fragment Ac-LKKTETQ, not full-length 43-residue thymosin β4 — the two are chemically different molecules, and almost all published Tβ4 efficacy work used the full protein.

Population

Commercial TB-500 product analysed by high-resolution mass spectrometry

Intervention

n/a — analytical characterisation

Comparator

Independently synthesised Ac-LKKTETQ reference standard

Limitations

One product lot from one supplier; gray-market vials are not a standardised article and later products may contain something else again.