The invention provides compounds of formula (I) or pharmaceutically acceptable salts thereof, wherein R.sup.a, R.sup.b, R.sup.c, R.sup.d, R.sup.e, R.sup.f and Y are as defined in the specification. The compounds are partial or full agonists at the growth hormone secretagogue (GHS) receptors. Pharmaceutical compositions comprising the compounds methods of preparing the compounds, uses of the compounds and methods involving the compounds are also provided.