[ Eq(Derivative(x1, t), (-1)*k6*k2*k1*x1*x3/x5/k6),
  Eq(Derivative(x2, t), (1*k6*k2*k1*x1*x3/x5 + (-1)*k6*k4*x2)/k6),
  Eq(Derivative(x3, t), (1*k6*k4*x2 + (-1)*k6*k3*x3)/k6),
  Eq(Derivative(x4, t), 1*k6*k3*x3/k6),
  Eq(Derivative(x5, t), 0/k6) ]