{HEAD ~ Z} is chosen from {TAIL ~ CR6} and CCOCNHR8, wherein R6 is alykl, arylalkyl, aryl, m cycloalkyl, heteroaryl, or ##STR73## wherein m=0 3 
is chosen from
{ HEAD ~ Z } is chosen from { TAIL ~ CR6 } and CCOCNHR8 , wherein R6 is alykl , arylalkyl , aryl , m cycloalkyl , heteroaryl , or # # STR73 # # wherein m=0 3
HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL 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