R3 represents methyl, ethyl, {TAIL ~ propyl}, isopropyl, butyl, isobutyl, sec.butyl, hydroxymethyl, {HEAD ~ hydroxyethyl}, mercaptomethyl, or methylthioethyl or 
R3 represents methyl , ethyl , { TAIL ~ propyl } , isopropyl , butyl , isobutyl , sec.butyl , hydroxymethyl , { HEAD ~ hydroxyethyl } , mercaptomethyl , or methylthioethyl or
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH