Cyclic lactam 'ALFA'-melanotropin analogues of ac-nle4-cyclo [asp5,d-phe7, lys10] 'ALFA'-melanocyte-stimulating hormone- (4-10)-nh2 with bulky aromatic amino acids at position 7 show high antagonist potency and selectivity at specific melanocortin receptors - Hruby, V J; Lu, D; Sharma, S D; Castrucci, Ana Maria de Lauro; Kesterson, R A; Al-Obeidi, F A; Hadley, M E; Cone, R D (Journal of Medicinal Chemistry, 1995)