Compounds of formula (I) are disclosed, wherein: A is a fibrinogen antagonist template; W is a linking moiety of the form -(CHRg)a-U-(CHRg)b-V-; Q?1, Q2, Q3 and Q4¿ are independently N or C-Ry, provided that no more than one of Q?1, Q2, Q3 and Q4¿ is N; R' is H or C¿1-6?alkyl, C3-7cycloalkyl-C0-6alkyl or Ar-C0-6alkyl; R?g¿ is H or C¿1-6?alkyl, Het-C0-6alkyl, C3-7cycloalkyl-C0-6alkyl or Ar-C0-6alkyl; R?k is Rg¿, -C(O)Rg or -C(O)ORg Ri is H, C¿1-6?alkyl, Het-C0-6alkyl, C3-7cycloalkyl-C0-6alkyl, Ar-C0-6alkyl, Het-C0-6alkyl-U'-C1-6alkyl, C3-7cycloalkyl-C0-6alkyl-U'-C1-6alkyl or Ar-C0-6alkyl-U'-C1-6alkyl; R?y¿ is H, halo, -ORg, -SRg, -CN, -NR?gRk, -NO¿2, -CF3, CF3S(O)r-, -CO2R?g, -CORg¿ or -CONRg2, or C1-6alkyl optionally substituted by halo, -ORg, -SRg, -CN, -NRgR'', -NO¿2?, -CF3, R'S(O)3-, -CO2R?g, -CORg¿ or -CONRg2; U and V are absent or CO, CRg2, C(=CRg2), S(O)c, O, NR?g, CRgORg, CRg(ORk)CRg¿2, CRg2CRg(ORk), C(O)CRg2, CRg2C(O), CONRi, NRiCO, OC(O), C(O)O, C(S)O, OC(S), C(S)NRg, NRgC(S), S(O)¿2?NR?g, NRgS(O)¿2N=N, NR?gNRg, NRgCRg¿2, NRgCRg2, CRg2O, OCRg2, CRg=CRg, C C, Ar or Het; a is 0, 1, 2 or 3; b is 0, 1 or 2; c is 0, 1 or 2; r is 0, 1 or 2; and u is 0 or 1; or pharmaceutically acceptable salts thereof, which are vitronectin receptor antagonists useful in the treatment of osteoporosis.