Piperazinebenzylamine derivatives from trans-4-(4-chlorophenyl)tetrahydrothiophene-3-carboxylic acid 6 and its S-oxide 7 and sulfone 8, and the tetrahydrofuran 9 and its two regioisomers 11 and 13 were synthesized and studied for their binding affinities at the human melanocortin-4 receptor. These five-membered ring constrained compounds possessed similar or lower potency compared to the acyclic analogs.