{HEAD ~ A process} 2, wherein R1, {TAIL ~ R2} and R3 are hydrogen and R4 is a lower alkyl group 
wherein
{ HEAD ~ A process } 2 , wherein R1 , { TAIL ~ R2 } and R3 are hydrogen and R4 is a lower alkyl group
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH