The open superstring 5-point amplitude revisited
  We derive the complete five-gluon scattering amplitude at tree level, within the context of Open Superstring theory. We find the general expression in terms of kinematic factors, and also find its complete expansion up to ${\cal O}({\alpha'}^3)$ terms. We use our scattering amplitude to test three non-equivalent ${\cal O}({\alpha'}^3)$ effective lagrangians that have recently been matter of some controversy. 
R. Medina, F. T. Brandt and F. R. Machado