R23 and {HEAD ~ R26} are each independently hydrogen, formyl, {TAIL ~ alkanoyl} of 2 7 carbon atoms, arylalkanoyl of 8 11 carbon atoms, aryloyl, or CO2 R27  
R23 and { HEAD ~ R26 } are each independently hydrogen , formyl , { TAIL ~ alkanoyl } of 2 7 carbon atoms , arylalkanoyl of 8 11 carbon atoms , aryloyl , or CO2 R27
OTH OTH HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH