[ Eq(Derivative(x1, t), (-k1)*(k7 + x8)*x1 - k2*x7*x1),
  Eq(Derivative(x2, t), k2*x7*x1 - k3*x7**k6*x2),
  Eq(Derivative(x3, t), k3*x7**k6*x2 - 4*k4*x3),
  Eq(Derivative(x4, t), 4*k4*x3 - 4*k4*x4),
  Eq(Derivative(x5, t), 4*k4*x4 - 4*k4*x5),
  Eq(Derivative(x6, t), 4*k4*x5 - 4*k4*x6),
  Eq(Derivative(x7, t), 4*k4*x6 - k5*x7),
  Eq(Derivative(x8, t), k5*x7),
  Eq(Derivative(x9, t), k1*(k7 + x8)*x1) ]