{HEAD ~ A compound} of the formula: ##STR38## wherein R1 and R2 are selected from the group consisting of hydrogen, methyl and ethyl, wherein R1 and {TAIL ~ R2} cannot both be hydrogen simultaneously 
{ HEAD ~ A compound } of the formula : # # STR38 # # wherein R1 and R2 are selected from the group consisting of hydrogen , methyl and ethyl , wherein R1 and { TAIL ~ R2 } can not both be hydrogen simultaneously
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH