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