We show that the colinear factorization properties of QCD amplitudes in the generalized Bjorken regime allow to relate in a simple way the amplitudes of exclusive reactions for spacelike and for timelike processes, at next to leading order in the strong coupling alpha_s. This leads, in particular, to simple formulae relating on the one hand the amplitudes for electroproduction of a photon or meson to the ones for photo- or meso-production of a lepton pair on the other hand. These relations will be useful in testing the relevance of the leading twist analysis of experimental data in terms of generalized parton distributions.
