R1 and R2 are independently H, C1 C18 alkyl; or R1 in combination with R2 forms {HEAD ~ a saturated 5 or 6 membered heterocycle} that is a piperidine, a morpholine, a pyrrolidine or {TAIL ~ a piperazine} 
R1 and R2 are independently H , C1 C18 alkyl ; or R1 in combination with R2 forms { HEAD ~ a saturated 5 or 6 membered heterocycle } that is a piperidine , a morpholine , a pyrrolidine or { TAIL ~ a piperazine }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL