alternatively, R2 and R3, together with the carbon atom to which they are attached, combine to form a C3 7 cycloalkyl, a C3 7 cycloalkenyl, or a 5–6 membered heterocyclic ring consisting of carbon atoms, {HEAD ~ 1 ring heteroatom} selected from O, N, NR10, and {TAIL ~ Sp}, and 0–2 double bonds 
alternatively , R2 and R3 , together with the carbon atom to which they are attached , combine to form a C3 7 cycloalkyl , a C3 7 cycloalkenyl , or a 5–6 membered heterocyclic ring consisting of carbon atoms , { HEAD ~ 1 ring heteroatom } selected from O , N , NR10 , and { TAIL ~ Sp } , and 0–2 double bonds
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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH