  We present a class of minimally extended standard models with the gauge group
$SU(3)_C \times SU(N)_L \times U(1)_X$ where for all $N \geq 3$, anomaly
cancelation requires three generations. At low energy, we recover the Standard
Model (SM), while at higher energies, there must exist quarks, leptons and
gauge bosons with electric charges shifted from their SM values by integer
multiples of the electron charge up to $ \pm [N/2] e$. Since the value N=5 is
the highest $N$ consistent with QCD asymptotic freedom, we elaborate on the
3-5-1 model.
