all the chemicals for the peptide synthesis were obtained , unless otherwise indicated , from fluka chemie gmbh ( buchs , switzerland ) in the greatest possible purity . the peptides were synthesised by means of conventional solid - phase peptide synthesis using the fmoc /′ bu strategy . all standard fmoc amino acids were obtained from multisyntech gmbh ( witten , germany ) or orpegen pharma gmbh ( heidelberg , germany ). trans - 4 - hydroxyproline ( t - 4 - hyp ) and tert - leucine were obtained from novabiochem ( merck biosciences gmbh , darmstadt , germany ). the peptides were synthesised on a 25 μmol scale with the aid of a syro 2000 peptide synthesis robot ( multisyntech gmbh , witten , germany ). to that end , 42 mg of leu - wang resin ( load : 0 . 6 mmol / g ) were weighed out per synthesis reactor and swollen for 30 minutes in dmf . after cleavage of the n - terminal fmoc protecting group , the peptides were synthesised with the following synthesis cycle ( table 2 ). for synthesis on a 100 μmol scale with the aid of a liberty microwave peptide synthesis robot ( cem gmbh , kamp - lintfort , germany ), 156 . 3 mg of commercially available leu - wang resin from novabiochem ( load : 0 . 64 mmol / g ) were weighed out per synthesis reactor and swollen for 30 minutes in dmf . after cleavage of the n - terminal fmoc protecting group , the peptides were inter alia synthesised with the following synthesis cycle ( table 3 ). there were used as side chain protecting groups triphenylmethyl ( trityl ) for cys , asn , his and gln , tert - butyl ether ( su ) for tyr , ser and thr , tert - butyl ester ( o t bu ) for asp and glu , ω - n - 2 , 2 , 4 , 6 , 7 - pentamethyldihydrobenzofuran - 5 - sulfonyl ( pbf ) for arg , tert - butyloxy - carbonyl ( boc ) for lys and orn . the temporary fmoc protecting group was cleaved with 40 % piperidine ( biosolve bv , valkenswaard , netherlands ) in dmf ( v / v ) for 5 minutes and again with fresh 20 % piperidine in dmf ( v / v ) for 10 minutes . the resin ( 1 eq .) was first swollen for 20 minutes in dmf . it was then incubated for 3 hours at room temperature and with shaking with hbtu in dmf ( 0 . 5 mol / l , 10 eq .) and nmm ( 10 eq .). the reaction solution was then renewed and the suspension was incubated for a further 4 hours . when the reaction was complete , the reaction solution was separated off and the resin was washed six times with dmf or dcm . the resin ( 1 eq .) was first swollen for 20 minutes in dmf . iodoacetic acid ( 8 eq .) and hobt in dmf ( 0 . 5 mol / l , 8 eq .) were then added , and the reaction was activated with dic ( 8 eq .). the reaction mixture was then incubated for 16 hours at room temperature in the dark and with shaking . when the reaction was complete , the reaction solution was separated off and the resin was washed six times with dmf or dcm and then dried . the completeness of the modification at the n - terminus of the peptide or of the side chain was checked by means of the kaiser test . to that end , some resin was incubated at 95 ° c . with 0 . 28 mol / l ninhydrin ( riedel de haen , seelze , germany ) in ethanol ( can roth gmbh + co . kg , karlsruhe , germany ), 0 . 2 mmol / l potassium cyanide in pyridine and 76 % phenol in ethanol in the ratio ( 1 : 1 : 2 ). if a blue colouration occurred , which indicates free primary amino groups , the coupling was repeated . because polyethylene glycol has hygroscopic properties , it was dried under a high vacuum before each coupling reaction . the following polyethylene glycol derivatives ( all iris biotech gmbh , marktredwitz , germany , & gt ; 95 % purity ) were used as starting materials for the couplings described below : a .) coupling of polyethylene glycol with a free acid group ( speg , e . g . for meo - peg - cooh ) via dic and hobt : the resin ( 1 eq .) was first swollen for 20 minutes in dmf . the polyethylene glycol derivative ( 5 eq .) dissolved in hobt / dmf ( 0 . 5 mol / l , 5 eq .) was then added , and the reaction was activated with dic ( 5 eq .). the reaction mixture was then incubated for one hour at rt and with shaking . dic ( 2 . 5 eq .) was then added again , and incubation was carried out for a further 30 minutes . when the reaction was complete , the reaction solution was separated off and the resin was washed six times with dmf . complete coupling was checked by means of the kaiser test . b .) coupling after activation of the polyethylene glycol , in particular for peg 5000 and greater : here , the polyethylene glycol derivative with a free acid group was first activated as n - hydroxysuccinimide ( nhs ) ester and then coupled in solution . to form the active ester , the polyethylene glycol ( 1 eq .) was incubated at room temperature , with shaking , with in each case 1 eq . of the dcc and n - hydroxysuccinimide previously dissolved in dmf until , after three hours , a fine precipitate formed . the peg active ester ( 1 eq .) dissolved in the supernatant was added to the peptide ( 0 . 9 eq .) and incubated at rt , with shaking , in pbs ( ph = 7 . 4 ) or dmf . the reaction was monitored by means of rp - hplc and maldi - tof - ms or by lc - ms . a thiol - derivatised polyethylene glycol ( e . g . meo - peg - sh ) ( 1 eq .) was added to the iodoacetylated peptide ( 4 eq .) in pbs ( ph = 7 . 4 ), the reaction solution was degassed , and incubation was carried out under an n 2 atmosphere at 4 ° c . for 18 hours . the progress of the reaction was monitored by means of rp - hplc and maldi - tof - ms . the pegylated peptides were obtained in a yield of from 25 to 40 % and characterised by means of rp - hplc and maldi - ms . when the synthesis of the peptides and optional modification were complete , the resins were washed carefully with dmf and dcm and dried . the resin - bonded peptides were cleaved for 4 hours at room temperature with a mixture of water , m - cresol , thioanisole and ethanedithiol ( 5 : 5 : 5 : 2 . 5 ) in 87 . 5 % trifluoroacetic acid ( tfa ), and at the same time the side chains were deprotected . the peptides and peptide derivatives were precipitated with cold diethyl ether and centrifuged off at 3000 × g . the pellet was washed twice with cold ether , dried and dissolved in 0 . 1 % aqueous tfa ( uv spectroscopy ). the samples were stored at − 20 ° c . the cleaved ( optionally modified ) peptides were purified by means of rp - hplc on an akta hplc system ( amersham bioscience gmbh , freiburg , germany ) with a jupiter c 18 5 μm 300 å , 250 × 10 mm or jupiter c 18 15 μm , 300 å , 250 × 21 mm column ( phenomenex inc ., torrance , usa ). as eluent there was used in each case 0 . 1 % aqueous tfa ( eluent a ) and 60 % aqueous acetonitrile ( biosolve bv , valkenswaard , netherlands ) with 0 . 1 % tfa ( eluent b ). a typical linear gradient began at 5 % b and the elution took place at a gradient of 1 % b per minute with a flow rate of 10 ml / min ( 250 × 21 mm column ) or 5 ml / min ( 250 × 10 mm column ). detection was at 220 , 230 and 240 nm . analysis of the purified peptides was carried out with the same hplc system with a jupiter c 18 5 μm , 300 å , 150 × 4 . 6 mm column ( phenomenex inc ., torrance , usa ). elution was carried out at a flow rate of 1 ml / min with a linear gradient of 5 - 95 % b in 30 minutes , and detection was at 220 nm . in addition , the purity was determined by means of matrix - assisted laser desorption / ionisation with time - of - flight mass spectrometry ( maldi - tof - ms ; 4700 proteomic analyzer , applied biosystems gmbh , darmstadt , germany ). to that end , 0 . 5 μl of peptide solution was co - crystallised with 0 . 5 μl of α - cyanohydroxycinnamic acid ( bruker daltonik gmbh ; bremen , germany ) as matrix ( 4 mg / ml in 60 % acetonitrile in 0 . 1 % aqueous tfa ). example 2 : determination of the minimum inhibitory concentrations and growth kinetics the minimum inhibitory concentrations ( mic ) of the peptides were determined in a double determination of triplicates with a positive control ( gentamycin ) and a negative control ( 0 . 9 % nacl solution ). to that end , the peptides were dissolved in water and diluted in a two - fold dilution series with 1 % aqueous soybean medium ( tsb ) in sterile 96 - well plates ( greiner bio - one gmbh ) from 128 μg / ml in twelve dilution steps to 62 . 5 ng / ml . overnight cultures of escherichia coli strain bl21ai were adjusted with 1 % tsb to about 1 . 5 × 10 7 colony forming units per ml . in each case 50 μl of peptide solution per well were then mixed with in each case 50 μl of the bacteria solution , in order to achieve a starting concentration of 4 × 10 5 bacteria per well . after incubation for 20 hours at 37 ° c ., the absorption at 595 nm was determined ( microplate reader , tecan trading ag ). the minimum inhibitory concentration was identified as the lowest peptide concentration at which no bacterial growth was demonstrated . in addition , the antibacterial activity was also determined in the presence of 25 % mouse serum . to that end , the mic values were determined as described above , but 25 μl of mouse serum were also added to each well before the incubation ( 25 % final concentration ). owing to the large difference in mass between the unmodified and the peg - coupled peptides , the mic is not given in the conventional unit μg / ml but in μmol / l . the results show that the presence of the peptide linker ( gar - onc 72 and gar - onc 120 ) or residues thereof remaining in the cleavage product ( api 137 ( sg ), api 300 ( sg ) and api 301 ( sg )) does not increase the mic or increases it only insignificantly . in the peg - modified peptides , the mic in tsb increases with the size of the peg . without serum ( tsb ), the peg - modified peptides exhibit an increased mic . in the serum , the peg - modified peptides have , however , a mic which is comparable with the unpegylated peptides . 30 μl of a 1 mg / ml peptide solution were diluted with 120 μl of water and , after addition of 50 of serum , incubated at 37 ° c . for 0 hours , 0 . 5 hour , 1 hour , 2 hours or 4 hours . alternatively , the peptide derivatives having a starting concentration of 3 mg / ml were diluted with serum to a final concentration of 15 μg / ml . according to the stability of the peptides , the samples were analysed at the times mentioned above or after 0 hours , 4 hours and 6 hours . the serum proteins were precipitated by addition of 50 μl of 15 % tca , and the supernatant was neutralised with 25 μl of 1 mol / l naoh . the samples were made up to 250 μl with 5 % b , 230 μl of the solution were transferred into a hplc vial , and 220 μl were injected . rp - hplc analysis was carried out with a linear acetonitrile gradient ( biosolve bv , valkenswaard , netherlands ) in the presence of 0 . 1 % trifluoroacetic acid ( tfa , uv grade , fluka chemie gmbh , buchs , switzerland ) as ion - pair reagent . the fractions were co - crystallised with α - cyanohydroxycinnamic acid ( bruker daltonik gmbh ; bremen , germany ) as matrix ( 4 mg / ml in 60 % acetonitrile in 0 . 1 % aqueous tfa ) and analysed with a tandem mass spectrometer ( maldi - tof / tof - ms , 4700 proteomics analyzer ; applied biosystems gmbh , weiterstadt , germany ) in positive - ion reflector mode . the amount of intact peptides and their degradation products or metabolites could thus be identified and quantified at the individual times . 25 % aqueous mouse serum , which was analysed in parallel for the same time intervals , was used as control . the half - lives ( or uncleaved peptide remaining after the indicated time ) relate in the case of the free peptides ( api 137 , api300 ( sg ) and api 301 ( sg )) to the cleavage site in the peptide ( downstream of arg - 16 ). in the case of the remaining derivatives , the values relate to the cleavage in the linker in the side chain with release of api 137 ( sg ), api300 ( sg ) and api 301 ( sg ) or of onc 72 and onc 110 .
the invention relates to modified antibiotic peptides , in particular derivatives of apidaecin and oncocin , preferably having increased stability , reduced immunoreaction , and improved pharmacokinetics . in the invention , the peptide antibiotics are reversibly protected by means of a linker having the polymer polyethylene glycol . the peptide linker contains a recognition sequence for trypsin - like serum proteases . in the apidaecin derivatives , the linker and the peg are bonded to a side chain . in the serum , the linker is cut by serum proteases and peg is separated off . the released peptide still contains remnants of the linker , which are still bonded to the amino group in the side chain . astonishingly , said remaining remnants of the linker impair the activity of the antimicrobial peptide only a little or not at all .