{HEAD ~ R2} represents C1 6 alkyl, phenyl, 1 3 phenyl or {TAIL ~ 1 4 COOR5}, or 
represents
{ HEAD ~ R2 } represents C1 6 alkyl , phenyl , 1 3 phenyl or { TAIL ~ 1 4 COOR5 } , or
HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH