Compounds I-III wherein U is CH, O, or S; Z is mono- or di-substituted carbon; R is (CH2)nCO2H, (CH2)nSO3H, (CH2)nPO3H2, (CH2)nNO2, CH(SCH3)3, esters; R1 is H, hydroxyalkyl, aminoalkyl, alkoxyalkyl; RR1 is O; n is 0-4; R2, R3 is H, hydroxyalkyl, aminoalkyl, alkoxyalkyl, haloalkyl; R4 is (CH2)nOH, (CH2)nNH2, substituted alkyl were prepd. as neuraminidase inhibitors. Thus, (1R,3R,4R,1'S)-(-)-(1'-acetylamino-2 '-ethyl)butyl-4-(aminoimino)methylaminocyclopentan-1-carboxylic acid was prepd. and tested in vitro as neuraminidase inhibitor (IC50<;1.mu.M).