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