The acylation of 4-hydroxypiperidine (I) with benzyl chloroformate (II) by means of triethylamine in dichloromethane gives 4-hydroxypiperidine-1-carboxylic acid benzyl ester (III), which is condensed with tert-butyl bromoacetate (IV) by means of tetrabutylammonium hydrogensulfate and NaOH in toluene/water, affording 2-[1-(benzyloxycarbonyl)piperidin-4-yloxy]acetic acid tert-butyl ester (V). The deprotection of (V) by hydrogenation with H2 over Pd/C in ethanol gives the piperidine (VI), which is condensed with N-(benzyloxycarbonyl)-4-O-tert-butyl-L-tyrosine (VII) by means of 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and N-methylmorpholine (NMM) in dichloromethane, yielding the expected condensation product (VIII). The deprotection of the amino group of (VIII) by hydrogenation as before affords (IX), which is N-acylated with 4-amidinobenzoyl chloride (X), prepared by reaction of 4-amidinobenzoic acid (XI) with SOCl2, giving the bis-tert-butylated product (XII). Finally, this compound is deprotected by means of trifluoroacetic acid in dichloromethane.

The acylation of 4-hydroxypiperidine (I) with benzyl chloroformate (II) by means of triethylamine in dichloromethane gives 4-hydroxypiperidine-1-carboxylic acid benzyl ester (III), which is condensed with tert-butyl bromoacetate (IV) by means of tetrabutylammonium hydrogensulfate and NaOH in toluene/water, affording 2-[1-(benzyloxycarbonyl)piperidin-4-yloxy]acetic acid tert-butyl ester (V). The deprotection of (V) by hydrogenation with H2 over Pd/C in ethanol gives the piperidine (VI), which is condensed with N-(benzyloxycarbonyl)-4-O-tert-butyl-L-tyrosine (VII) by means of 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and N-methylmorpholine (NMM) in dichloromethane, yielding the expected condensation product (VIII). The deprotection of the amino group of (VIII) by hydrogenation as before affords (IX), which is N-acylated with 4-amidinobenzoyl chloride (X), prepared by reaction of 4-amidinobenzoic acid (XI) with SOCl2, giving the bis-tert-butylated product (XII). Finally, this compound is deprotected by means of trifluoroacetic acid in dichloromethane.

2) The reaction of 4-hydroxypiperidine (VII) with benzyl chloroformate (VIII) by means of triethylamine in dichloromethane gives the expected benzyloxycarbonyl derivative (IX), which is condensed with tert-butyl 2-bromoacetate (X) by means of tetrabutylammonium bisulfate and NaOH, yielding 2-[1-(benzyloxycarbonyl)piperidin-4-yloxy]acetic acid tert-butyl ester (XI). The deprotection of (XI) as ususal affords 2-(4-piperidinyloxy)acetic acid tert-butyl ester (XII), which is condensed with N-(benzyloxycarbonyl)-L-alanine (XIII) by means of 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and N-methyl-morpholine (NMM) in dichloromethane to yield the acylated piperidine (XIV). The deprotection of (XIV) as usual affords compound (XV), which is acylated at the free amino group with 4-cyanobenzoyl chloride (V) and tetrabutylammonium bisulfate to give 2-[1-[N-(4-cyanobenzoyl)-L-alanyl]piperidin-4-yloxy]acetic acid tert-butyl ester (XVI). The reaction of the cyano group of (XVI) with hydroxylamine affords compound (XVII) with a hydroxyamidino substituent. Finally, the tert-butyl ester group of (XVII) is converted in ethyl ester by hydrolysis with hot fomic acid to the corresponding acetic acid (XVIII) and subsequent esterification with ethanol/H2SO4.

The acylation of 4-hydroxypiperidine (I) with benzyl chloroformate (II) by means of triethylamine in dichloromethane gives 4-hydroxypiperidine-1-carboxylic acid benzyl ester (III), which is condensed with tert-butyl bromoacetate (IV) by means of tetrabutylammonium hydrogensulfate and NaOH in toluene/water, affording 2-[1-(benzyloxycarbonyl)piperidin-4-yloxy]acetic acid tert-butyl ester (V). The deprotection of (V) by hydrogenation with H2 over Pd/C in ethanol gives the piperidine (VI), which is condensed with N-(benzyloxycarbonyl)-4-O-tert-butyl-L-tyrosine (VII) by means of 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and N-methylmorpholine (NMM) in dichloromethane, yielding the expected condensation product (VIII). The deprotection of the amino group of (VIII) by hydrogenation as before affords (IX), which is N-acylated with 4-amidinobenzoyl chloride (X), prepared by reaction of 4-amidinobenzoic acid (XI) with SOCl2, giving the bis-tert-butylated product (XII). Finally, this compound is deprotected by means of trifluoroacetic acid in dichloromethane.