  We analyze the Next-to-minimal supersymmetric standard model with Grand
unification boundary conditions under current theoretical and experimental
constraints. We compute the mass spectrum of the model and focus on the three
lightest particles in the Higgs sector (two CP-even scalars, $h_1, h_2$, and
one CP-odd, $a_1$). The reduced couplings of such particles, singlet-doublet
components, their branching ratios to bosons, and reduced cross-section to
photons and massive gauge bosons via gluon fusion are thoroughly and
systematically scrutinized. Our analysis is focused on the parameter space
where the singlet-doublet coupling $\lambda$ is as large as possible (keeping
the perturbativity bound intact) and the ratio between the vacuum expectation
values of the up-type and down-type Higgses ($\tan{\beta}$) is as small as
possible, which is the region representing the most natural case of the NMSSM.
We show the impact of recent constraints from the LHC on the SM-Higgs couplings
to bosons and fermions on the parameter space of the model and the consequent
implications on the Higgs sector. The results show that while the model is
still able to account for current data and provide an opportunity for discovery
of extended Higgs sectors, recent LHC Higgs couplings constraints rule-out
parts of the parameter space where $h_2$ (non-SM-like) and $a_1$ are
non-singlet with masses below ~400 GeV.
