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,1S)-(-)-(1-acetylamino-2 -ethyl)butyl-4-(aminoimino)methylaminocyclopentan-1-carboxylic acid was prepd. and tested in vitro as neuraminidase inhibitor (IC50<1.mu.M).