4-{[1,1'-biphenyl]-4-carbonyl}-8-methyl-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

8-ethyl-4-(4-methylbenzoyl)-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

8-ethyl-4-(4-methyl-3-nitrobenzoyl)-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

4-(3,5-dichlorobenzoyl)-8-ethyl-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

4-(2-phenylacetyl)-8-propyl-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

4-(2-phenylbutanoyl)-8-propyl-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

4-(3-chlorobenzoyl)-8-propyl-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

4-(3-methylbenzoyl)-8-propyl-1-oxa-4,8-diazaspiro[4.5]decane-3-carboxylic acid

8-tert-butyl-4-(2-phenylacetyl)-1-oxa-4-azaspiro[4.5]decane-3-carboxylic acid

8-tert-butyl-4-(naphthalene-1-carbonyl)-1-oxa-4-azaspiro[4.5]decane-3-carboxylic acid

8-tert-butyl-4-(2,5-difluorobenzoyl)-1-oxa-4-azaspiro[4.5]decane-3-carboxylic acid