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