Compounds of formula (I) STR1 wherein A1 is C or N; E is a five- or six-membered heteroaromatic or six-membered aromatic ring optionally substituted by R3 or R4 ; X1 --X2 is CHR1 --CH, CR1 =CH, NR1 --CH, S(O)u --CH or O--CH; X3 is CR5 R5 ', NR5, S(O)u or O; R2 is --OR', --NR'R", --NR'SO2 R'", --NR'OR', --OCR'2 C(O)OR', --OCR'2 OC(O)--R', --OCR'2 C(O)NR'2, CF3 or --COCR'2 R2 '; R3, R4 and R7 are independently H, halo, --OR12, --SR12, --CN, --NR'R12, --NO2, --CF3, CF3 S(O)r --, --CO2 R', --CONR'2, R14 --C0-6 alky-, R14 --C1-6 oxoalkyl-, R14 --C2-6 alkenyl-, R14 --C2-6 alkynyl-, R14 --C0-6 alkyloxy-, R14 --C0-6 alkylamino- or R14 --C0-6 alkyl--S(O)r --; R6 is W--(CR'2)q --Z--(CR'R10)--U--(CR'2)s --V-- or W'--(CR'2)q --U--(CR'2)s -- U and V are absent or CO, CR'2, C(=CR152), S(O)n, O, NR15, CR15 'OR15, CR'(OR")CR'2, CR'2 CR'(OR") C(O)CR'2, CR152 C(O), CONR15, NR15 CO, OC(O), C(O)O, C(S)O, OC(S), C(S)NR15, NR15 C(S), SO2 NR15, NR15 SO2, N=N, NR15 NR15, NR15 CR152, NR15 CR152, CR152 O, OCR152, C$(m)ZC, CR15 =CR15, Het, or Ar, provided that U and V are not simultaneously absent, and W and W' are a nitrogen-containing substituent, and integrin receptor antagonists.