1,274,908. Aminocyclopentane carboxylic acid derivatives. AMERICAN HOME PRODUCTS CORP. 18 Aug., 1969 [20 Aug., 1968; 3 June, 1969], No. 41101/69. Heading C2C. Novel compounds of Formula I in which R<SP>1</SP> is aliphatic or aryl sulphonylamido: methyloxy; aryloxy; trimethylammoniumethoxy; OCHR<SP>3</SP>OR<SP>4</SP>, where R<SP>3</SP> is hydrogen or lower alkyl and R<SP>4</SP> is lower alkyl or COR<SP>5</SP>, where R<SP>5</SP> is lower alkyl, phenyl or chlorophenyl; where R<SP>6</SP> is lower alkyl and R<SP>7</SP> is methylol or carboloweralkyloxy; or OCH 2 -NG, where G is and R<SP>2</SP> is hydrogen, purinecarbonyl, alkyl, aryl, arylalkyl or their pharmaceutically acceptable acid addition salts are prepared by esterification of the corresponding compound wherein R<SP>1</SP> is OH, or by sulphonamidation of the corresponding compound where R<SP>1</SP>OH or an ester thereof, or by alkylation, aralkylation, arylation or acylation of the corresponding compound, where R<SP>2</SP> is H. (Lower denotes groups containing 1 to 7 carbon atoms, aryl denotes groups optionally substituted by alkyl or halogen substituents.) 1 - Amino - 1 - cyclopentanecarboxylic acid is prepared by reaction of cyclopentanone, ammonium carbonate and HCN and then acidification. p-Nitrophenyl esters of compounds of Formula I, where R<SP>1</SP> is OH and R<SP>2</SP> is benzyloxycarbonyl are prepared by standard methods. Pharmaceutical compositions in conventional forms for oral and parenteral administration and having anti-inflammatory and immunosuppressive activity comprise a novel compound of Formula I and a carrier or diluent therefor.