Begin by defining a five-membered ring (called Ring A) with two nitrogen atoms at positions A1 and A2. A1 is substituted and bears no hydrogen, while A2 carries one hydrogen. The three intervening ring atoms are carbons A3, A4, and A5.
- At A1 (the substituted nitrogen), there is a six-membered cyclohexane ring (Ring B). Label its attachment point to A1 as B1, which is a chiral center with S configuration. The adjacent carbon atom of B1 carries a nitrile substituent (a carbon triple-bonded to a nitrogen) and is also a chiral center with an S configuration.
- Shared with A4 and A5, there is an aromatic ring (Ring C, pyridine ring) comprising six members (five carbons and one nitrogen) fused with Ring A. In Ring C, designate the fusion point corresponding to A4 as C3 and the fusion point corresponding to A5 as C4, with the nitrogen in Ring C at position 1. The ring carbon at C2 carries a hydroxyl group.
- At A3 of Ring A, there is a double bond to an exocyclic nitrogen, which in turn is bonded to a six-carbon ring (Ring D). Ring D has two double bonds. Suppose the carbon connected to the nitrogen is numbered as C1, with double bonds between C2 and C3, and between C4 and C5, and a methyl substituent on C4.
