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