alternatively, R4 and R5, together with {TAIL ~ 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, 1 ring heteroatom selected from {HEAD ~ O}, N, NR10, and Sp, and 0–2 double bonds 
alternatively , R4 and R5 , together with { TAIL ~ 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 , 1 ring heteroatom selected from { HEAD ~ O } , N , NR10 , and Sp , and 0–2 double bonds
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH