[ Eq(Derivative(x1, t), (1*k11*k1/(1 + k2*x4) + (-1)*k11*k3*x1 + (-1)*k11*k4*x1)/k11),
  Eq(Derivative(x2, t), (1*k11*k3*x1 + (-1)*k11*k5*x2 + (-1)*k11*k6*x2)/k11),
  Eq(Derivative(x3, t), ((-1)*k11*k6*x3 + 1*k11*k6*x2 + (-1)*k11*k5*x3)/k11),
  Eq(Derivative(x4, t), (1*k11*k6*x3 + (-1)*k11*k7*x4 + 1*k11*k8*x5 + 1*k11*k10*x4*x5)/k11),
  Eq(Derivative(x5, t), (1*k11*k7*x4 + (-1)*k11*k8*x5 + (-1)*k11*k10*x4*x5 + (-1)*k11*k9*x5)/k11) ]