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