  A study of the meson-baryon interaction in the $S=-1$ sector is performed,
employing a chiral SU(3) lagrangian up to next-to-leading order (NLO) and
implementing unitarization in coupled channels. The model is constrained by a
large set of experimental data, paying a especial attention to processes that
are sensitive to the NLO contributions, such as the $K^- p\to K^+\Xi^-,
K^0\Xi^0$ reactions. The consideration of additional cross sections in single
isospin channels, $K^-p\to \eta\Lambda, \eta\Sigma$, has been found to provide
more homogeneous and reliable values of the low-energy constants, the stability
of which has also been tested by the inclusion of explicit resonant terms.
Predictions for new isospin filtering processes, like the $I=1$ $K^0_L p \to
K^+ \Xi^0$ reaction that could be measured at the proposed secondary $K^0_L$
beam at Jlab, or the weak decay of the $\Lambda_b$ into a $J/\Psi$ and
different meson-baryon pairs in $I=0$, available at LHCb, are presented. The
measurement of such reactions would put valuable constraints on the chiral
models describing the $S=-1$ meson-baryon interaction.
