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