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