Prostaglandin E2 (PGE2) has been known as a metabolite in the arachidonic acid cascade.  It has been known that PGE2 possesses cyto-protective activity, uterine contractile activity, a pain-inducing effect, a promoting effect on digestive peristalsis, an awaking effect, a suppressive effect on gastric acid secretion, hypotensive activity, and diuretic activity. 
In the recent study, it was found that PGE2 receptor was divided into some subtypes, which possesses different physical roles from each other.  At present, four receptor subtypes are known and they are called EP1, EP2, EP3 and EP4 respectively [J. Lipid Mediators Cell Signaling, 12, 379-391 (1995)]. 
Among these subtypes, EP3 receptor was believed to be involved in signal transduction of peripheral nerve, control of exothermal reaction in central nerve, formation of memory by expressing in cerebral neuron, vascularization, reabsorption of urine by expressing in renal tubular, uterine contraction, production of ACTH, platelet aggregation.  Besides, it was expressed in vascular smooth muscle, heart and gastrointestinal tract also.  EP4 receptor was believed to be involved in suppression of TNF-α production and induction of IL-10 production. 
So the compounds which can bind to EP3 receptor and/or EP4 receptor strongly and show the antagonizing activity, are useful for the prevention and/or treatment of diseases induced by excess activation of EP3 receptor and/or EP4 receptor, for example, pain such as cancerous pain, fractural pain, pain following surgical and dental procedures; allodynia, hyperalgesia, pruritus, urticaria, atopic dermatitis, contact dermatitis, rhus dermatitis, allergic conjunctivitis, various symptoms by treating with dialysis, asthma, rhinitis, sneeze, urinary frequency such as neurogenic bladder, neurogenic bladder, irritant bladder, unstable bladder, urinary frequency that originate with prostate-gland enlargement; urinary disturbance, ejaculatory failure, fever, systemic inflammatory response syndrome, learning disturbance, Alzheimer's disease, angiogenesis, cancer such as formulation of cancer, growth of cancer and metastasis of cancer; retinopathy, patch of red, erythematous patches, achromoderma, pigmented spot, scald, burn, burn by steroid, renal failure, nephropathy, acute nephritis, chronic nephritis, abnormal blood levels of electrolytes, threatened premature delivery, abortion threatened, hypermenorrhea, dysmenorrhea, uterine fibroids, premenstrual syndrome, reproductive disorder, stress, anxiety disorders, depression, psychosomatic disorder, mental disorder, thrombosis, embolism, transient ischemia attack, cerebral infarction, atheroma, organ transplant, myocardial infarction, cardiac failure, hypertension, arteriosclerosis, circulatory failure and circulatory failure induced ulcer, neuropathies, vascular dementia, edema, various arthritis, rheumatism, diarrhea, constipation, disorder of bilious excretion, ulcerative colitis, Crohn's disease, irritable bowel syndrome, alleviation of rebound phenomenon after steroid, dose reduction of steroid and adjunct for steroid withdrawal and/or bone diseases such as osteoporosis, rheumatoid arthritis, osteoarthritis, abnormal bone formation; cancer such as formation of cancer, proliferation of cancer, metastasis of cancer to organs and to bones and hypercalcemia induced metastasis to bones of cancer; systemic granuloma, immunological diseases such as ALS, multiple sclerosis, Sjoegren's syndrome, systemic lupus erythematosus, AIDS; allergy such as allergic conjunctivitis, allergic rhinitis, contact dermatitis, psoriasis; atopy such as atopic dermatitis; asthma, pyorrhea, gingivitis, periodontitis, neuronal cell death, Alzheimer's disease, pulmonary injury, hepatopathy, acute hepatopathy, nephritis, renal failure, myocardial ischemia, Kawasaki disease, scald, ulcerative colitis, Crohn's disease, multiple organ failure, chronic headache such as migraine headache, tension-type headache or mixed headache thereof, cluster headache; pain, angiogenesis, angiitis, venous insufficiency, varicose veins, anal fistula, diabetes insipidus, stress, endometriosis, adenomyosis of the uterus, neonatal patent ductus arteriosus, cholelithiasis etc.  Moreover, it relates to sleeping disorder and platelet aggregation, so the compounds are considered to be useful for them. 
As a compound useful for a treatment of a disease related prostaglandin E receptor, for example, (A) in a specification of WO 99/47497, a compound of formula (A):
wherein HETa is a 5- to 12-membered mono- or bi-aromatic ring; Aa is a group of one or two atoms; Xa is 5- to 10-membered mono- or bi-aryl, heteroaryl, and the rings may be substituted with R14a and R15a; Ba is —(C(R18a)2)pa—Ya—(C(R18a)qa—; R1a, R2a and R3a are hydrogen, halogen, lower alkyl, lower alkenyl, lower alkynyl, etc.;  and(B) in a specification of WO 00/20371, a compound of formula (B)
wherein Ar1b is aryl or heteroaryl; Wb is a 3- to 6-membered linking chain containing 0-2 of a hetero atom(s); Ar2b is aryl or heteroaryl which may be substituted with R3b; R3b is hydrogen, lower alkyl, lower alkenyl, lower alkynyl, CHF2, CF3, halogen, halo(C1-6) alkyl, N(R5b)2, cyano, nitro, C(R6b)3; Xb is a linking chain; Qb is COOH, tetrazole, SO3H, hydroxamic acid, CONHSO2R12b, SO2NHCOR12b; were described.