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