  A survey of the inner 8$^\circ \times 1^\circ$ of the Galactic plane toward
the Galactic center has been carried out at the 1720 MHz transition of OH
molecule using the VLA in its D configuration with a resolution of
$\approx70''\times45''$. The detection of compact 1720 MHz OH masers associated
with three supernova remnants G357.7+0.3, G1.13--0.1 (Sgr D) and G1.4--0.1 as
well as new extended maser line emission from G357.7+0.3 and G357.7--0.1 (the
Tornado Nebula) were then followed up by A-array observations with spectral and
spatial resolutions of 0.3 \kms and $\approx3''\times2''$, respectively.
  The 1720 MHz OH maser line emission is considered to be a powerful shock
diagnostic and is collisionally pumped by H$_2$ molecules at the site where
C-type supernova shocks drive into adjacent molecular clouds. The new
observations show clear evidence of extended features coincident with compact
and bright masers, the best example of which is a coherent feature over a scale
of about 20 pc surrounding the shell of the SNR G357.7+0.3. We argue that this
remarkable feature is an OH maser and is physically associated with the
remnant. This implies that the ambient molecular cloud is uniform in its
density and temperature with restricted range of pumping conditions and
survives the passage of a large-scale shock front.
