Relating the Green-Schwarz and Pure Spinor Formalisms for the   Superstring
  Although it is not known how to covariantly quantize the Green-Schwarz (GS) superstring, there exists a semi-light-cone gauge choice in which the GS superstring can be quantized in a conformally invariant manner. In this paper, we prove that BRST quantization of the GS superstring in semi-light-cone gauge is equivalent to BRST quantization using the pure spinor formalism for the superstring. 
Nathan Berkovits, Dafni Z. Marchioro (IFT/UNESP - Sao Paulo)