R3 and R4 are independently selected from hydrogen, or an aliphatic, carbocyclic, or heterocyclic group, or R3 and R4, or R3 or R4 and {HEAD ~ Z3} together may form a 5, 6, or 7 membered carbocylic or {TAIL ~ heterocyclic ring}; and 
form
R3 and R4 are independently selected from hydrogen , or an aliphatic , carbocyclic , or heterocyclic group , or R3 and R4 , or R3 or R4 and { HEAD ~ Z3 } together may form a 5 , 6 , or 7 membered carbocylic or { TAIL ~ heterocyclic ring } ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH