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