{HEAD ~ A compound} 15, wherein Ra, {TAIL ~ Rb} and Rc are each hydrogen 
wherein
{ HEAD ~ A compound } 15 , wherein Ra , { TAIL ~ Rb } and Rc are each hydrogen
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH