R11 is H, CH3, a carboxylic acid or {HEAD ~ a biologically compatible salt} of {TAIL ~ a carboxylic acid} 
of
R11 is H , CH3 , a carboxylic acid or { HEAD ~ a biologically compatible salt } of { TAIL ~ a carboxylic acid }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL