R6 is lower alkyl, {TAIL ~ phenyl}, {HEAD ~ R3 phenyl}, benzyl or R3 benzyl 
R6 is lower alkyl , { TAIL ~ phenyl } , { HEAD ~ R3 phenyl } , benzyl or R3 benzyl
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH