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