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