  We present the analytic computation of the master integrals associated to
certain two-loop non-planar topologies, which are needed to complete the
evaluation of the last two color coefficients for the top-pair production in
the quark-annihilation channel, which are not yet known analytically. The
master integrals have been computed exploiting the differential equations
method in canonical form. The solution is given as a series expansion in the
dimensional regularization parameter through to weight four, the expansion
coefficients are given in terms of multiple polylogarithms.
