1. Begin with a pyridine ring (six-membered aromatic, nitrogen at position 1).

2. Substitution pattern on the pyridine  
   - Position 2 (alpha to the ring nitrogen): an -NH- linkage to a benzene ring (see item 3).  
   - Position 5 (meta to the nitrogen): an ethyl group -CH2-CH3.  
   - All other ring positions are hydrogen.

3. The -NH-benzene fragment  
   - The nitrogen is bonded to position 2 of the pyridine and to carbon-1 of a benzene ring.  
   - The benzene ring is 1,4-disubstituted:  
     - Carbon-1 carries the -NH- bond to the pyridine.  
     - Carbon-4 (para) carries an -O-aryl substituent (see item 4).  
     - Carbons 2, 3, 5 and 6 are hydrogen.

4. The -O-aryl substituent on the benzene is a pyrazine ring (1,4-diazine: six-membered aromatic with nitrogens at positions 1 and 4).  
   - The linker oxygen from the benzene ring is attached to carbon-2 of the pyrazine.  
   - Carbon-3 of the pyrazine is bonded to carbon-1 of a saturated heterocycle (item 5).  
   - The remaining pyrazine carbons are hydrogens.

5. Saturated heterocycle attached to the pyrazine  
   - A tetrahydropyran ring (six-membered, one oxygen).  
   - Number it so that the oxygen is position 4.  
   - Carbon-1 (para to the oxygen) is the atom joined to carbon-3 of the pyrazine.  
   - The tetrahydropyran ring bears no other substituents.

This fully specifies the structure.