RegEx Help match string except when

I presume its using Multiline to match, if so I'd expect this to work:

^interface.*\n\s+description DS[13][\w-]+\d+[^\.]\d+$

is this for policy rules?
if so, it might be easier to use "match block" which would search each interface block of code ->
start of block:
   ^interface s.*

end of block:
 ^!
where ^ means beginning of line

then your logic would be
regex matching:
  description DS[1,3]\.[0-9]

you'll have to tweak for your specific env, but hopefully that helps

Thank you.  This matched all my WAN interfaces perfectly and excluded all interfaces bound into a mlppp interface.

^interface.*\n\sdescription DS[13][\w-]+\d+[^\.\d]+$