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