  We perform infrared factorization of differential rates of radiative and
semileptonic inclusive decays of the B meson in the end-point region of photon
and charged lepton spectrum, respectively, in the leading heavy quark mass
limit. We find that the differential rates are expressed in terms of hard, jet
and soft functions, which satisfy evolution equations. Solving these equations,
we find expressions for the moments of the differential rates in their
end-point regions, which take into account all leading and nonleading
logarithmic corrections in perturbation theory, as well as large
nonperturbative power corrections. Expanded to the one-loop level, our
predictions coincide with the results of existing lowest order calculations for
B->\gamma X_s and B->l\barnu X_u. Nonperturbative corrections appear in our
formalism from the boundary value of the soft function in the evolution
equation. The soft function is a universal process-independent function, which
describes the distribution of the b quark in the B meson. Its behavior in the
end-point region is governed by the nonperturbative asymptotics of a Wilson
line expectation value. By considering the contributions of infrared
renormalons, we find an ansatz for the Wilson line, which leads to a Gaussian
model for the heavy quark distribution function.
