$sting =~
  m{\b        # word boundary
   (           
     \S+      # word before '('
     \s*      # spaces if any
     \(
      [^\)]+  # '(' inside of ')'
     \)
   )
   [^\)]*     # some not ')' chars if any 
   $          # end of string ancor
   }x;

$result = $1;