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