\chemfig{
            \mcfatomno{7}% 7
     -[:150]\mcfatomno{5}% 5
     -[:210]\mcfbelow{N}{\mcfatomno{4}}% 4
     -[:150]\mcfatomno{3}% 3
     =_[:90]\mcfatomno{2}% 2
               (
         -[:150]\mcfatomno{9}% 9
         -[:210]\mcfbelow{O}{\mcfatomno{10}}% 10
         -[:180]\mcfright{P}{\mcfatomno{11}}% 11
                   (
             -[:270]\mcfright{O}{\mcfatomno{13}}% 13
                   )
                   (
              -[:90]\mcfright{O}{\mcfatomno{14}}% 14
                   )
         =[:180]\mcfleft{\mcfatomno{12}}{O}% 12
               )
      -[:30]\mcfatomno{1}% 1
               (
          =[:90]\mcfatomno{15}% 15
          -[:30]\mcfright{N}{\mcfatomno{16}}% 16
          =[:90]\mcfatomno{17}% 17
                   (
             -[:150]\mcfatomno{19}% 19
                   )
          -[:30]\mcfatomno{18}% 18
                   (
             -[:330]\mcfright{O}{\mcfatomno{21}}% 21
                   )
          =[:90]\mcfright{O}{\mcfatomno{20}}% 20
               )
     -[:330]\mcfatomno{6}% 6
               (
          -[:30]\mcfright{O}{\mcfatomno{8}}% 8
               )
    =_[:270]\phantom{5}% -> 5
}