{HEAD ~ The substructure R} represents one of a halogen, —SH, —SZ, —S—S M L C2, wherein {TAIL ~ Z} represents a thiol protecting group 
{ HEAD ~ The substructure R } represents one of a halogen , — SH , — SZ , — S — S M L C2 , wherein { TAIL ~ Z } represents a thiol protecting group
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH