each of Am is independently {HEAD ~ a moiety} based on {TAIL ~ an amino acid} or on an amino acid derivative, or on a number of amino acids or derivatives thereof 
based on
each of Am is independently { HEAD ~ a moiety } based on { TAIL ~ an amino acid } or on an amino acid derivative , or on a number of amino acids or derivatives thereof
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH