The Gauge Theory of the de-Sitter Group and Ashtekar Formulation
  By adding the Pontrjagin topological invariant to the gauge theory of the de Sitter group proposed by MacDowell and Mansouri we obtain an action quadratic in the field-strengths, of the Chern-Simons type, from which the Ashtekar formulation is derived. 
J.A. Nieto, O. Obreg\'on and J. Socorro