{HEAD ~ R5} represents carboxy; and the carbon atoms marked by and are in {TAIL ~ R or S configuration} 
{ HEAD ~ R5 } represents carboxy ; and the carbon atoms marked by and are in { TAIL ~ R or S configuration }
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL