We present a preliminary measurement of the time-dependent CP asymmetries in decays of neutral B mesons to the final states D*^±p^± using approximately 82 million BB events collected by the BaBar experiment at the PEPII storage ring. Events containing these decays are selected with a partial reconstruction technique, in which only the high momentum p^± and the low momentum pion from the D*^± decay are reconstructed. The flavor of the other B meson in the event is tagged using the information from kaon and lepton candidates. We measure the time-dependent CP asymmetry A = -0.063 +/- 0.024 (stat.) +/- 0.017 (syst.). We interpret these results in terms of the angles of the unitarity triangle to set a bound on |sin(2b + g)|.