The compounds have the formula: ##STR1## wherein: {HEAD ~ the dashed line} indicates {TAIL ~ either the 4,5} unsaturated or the 4,5 dihydrofuranone ring 
The compounds have the formula : # # STR1 # # wherein : { HEAD ~ the dashed line } indicates { TAIL ~ either the 4,5 } unsaturated or the 4,5 dihydrofuranone ring
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH