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