one skilled in the art can , based on the description herein , utilize the present invention to its fullest extent . the following specific embodiments are , therefore , to be construed as merely illustrations of the invention and is not meant to be construed as limiting the full scope of the invention . 4 - methylbenzhydrylamine hydrochloride resin ( 0 . 25 or 0 . 5 mequiv g − 1 ) was obtained from advanced chemtech inc ., louisville , ky . n a tert - butyloxycarbonyl ( boc ) protected amino acids were purchased from bachem inc ., torrance , calif ., advanced chemtech inc ., and synthetech inc ., albany , oreg . the reactive side - chains of the amino acids were masked with one of the following groups : cys , 4 - methylbenzyloxycarbonyl ; lys , 2 - chlorobenzyloxycarbonyl ; thr , o - benzyl ; tyr , o - 2 , 6 - dichlorobenzyl . all reagents and solvents were acs grade or better and were used without further purification . compounds of the present invention , e . g ., compounds of formula ( i ) can be and were synthesized on 4 - methylbenzhydrylamine functionalized , 1 % cross - linked polystyrene resin ( 0 . 25 or 0 . 5 mequiv g − 1 ), in 0 . 25 mmol scale on an advanced chemtech ( model 200 ) synthesizer , using the following protocol : deblocking , 40 % tfa ( 2 min , 20 min ); dcm wash cycle ( three washes ); neutralization , 10 % diea ( 1 min , 5 min ); dmf wash cycle ; dcm wash cycle ( two washes ); double coupling ; first with 1 , 3 - diisopropyl carbodiimide esters ( 3 equiv . ), 30 min in dcm ; dcm wash ( three washes ); second coupling with preformed tbtu esters ( 3 equiv . ), 90 min in dmf , with a catalytic amount of diea ; dmf wash ( one wash ); dcm wash ( three washes ). coupling reactions were monitored qualitatively with the ninhydrin test . n ∝ - protection . after deblocking the amino group at the desired methylation site , the resin was suspended in dcm ( 20 ml ). to this suspension , collidine ( 3 equiv .) and o - nitrobenzenesulfonyl chloride ( 3 equiv .) were added and the mixture was shaken using advanced chemtech ( model 200 ) synthesizer for 2 h . then the resin was subjected to dcm wash ( 2 washes ) and dmf wash ( 3 washes ). protection was monitored qualitatively by the ninhydrin test . n ∝ - methylation . the o - nitrobenzenesulfonamide protected resin was suspended in dmf ( 20 ml ), to which mtbd ( 3 equiv .) and methyl 4 - nitrobenzenesulfonate or dimethyl sulfate ( for cys 11 ) were added . the mixture was shaken using advanced chemtech ( model 200 ) synthesizer for 0 . 5 h and the resin was subjected to dmf wash ( 4 washes ). n ∝ - me deprotection . once the desired residue was methylated , the resin was again suspended in dmf ( 20 ml ). dbu ( 3 equiv .) and 2 - mercaptoethanol ( 3 equiv .) were added to the suspension and the mixture was agitated for 0 . 5 h in advanced chemtech ( model 200 ) synthesizer . then the resin was thoroughly washed with dmf ( 5 washes ). peptide cleavage . the peptides were cleaved from the resin support with simultaneous side - chain deprotection by acidolysis using anhydrous hydrogen fluoride containing the scavenger anisole (˜ 30 % v / v ) for 45 min at 0 ° c . the peptides were cyclized in 90 % acetic acid (˜ 600 ml ) with a slight excess of i 2 ( 15 min ). excess i 2 was then removed by the addition of ascorbic acid . purification . the crude peptides were purified by preparative reverse phase - high performance liquid chromatography ( rp - hplc ) on c - 18 bonded silica gel using axial compression columns ( dynamax - 300 å , 5 or 8 μm , 21 . 4 × 250 mm ). a linear gradient elution system at a flow rate of 20 ml min − 1 was employed : a ; 0 . 1 % tfa , b ; 0 . 1 % tfa in 80 % mecn , 20 % b to 50 % b at 1 % min − 1 . the separations were monitored by analytical rp - hplc at 215 nm . the fractions containing the product were pooled , concentrated in vacuo and subjected to lyophilization . each peptide was obtained as a fluffy white powder of constant weight by lyophilization from aqueous acetic acid . the purity of the final peptides was assessed at 215 nm by analytical rp - hplc . analytical rp - hplcs were recorded using a vydac c - 18 support ( 4 . 6 250 mm , 5 mm , 300 å pore size , liquid separations group ). the linear gradient system was used at a flow rate of 1 . 5 ml min − 1 : hplc - 1 , a , 0 . 1 % tfa ; b , 0 . 1 % tfa in 80 % mecn ; 20 % b to 50 % b at 1 % min − 1 ; hplc - 2 , c , 5 % mecn in teap ( 0 . 1 m , ph 3 ); d , 20 % c in mecn , 10 % d to 70 % d at 1 % min − 1 . column eluent was monitored at 215 nm . the retention time and purity of each peptide was assessed by the rainin dynamax hplc method manager . amino acid analysis . the peptides were hydrolyzed in vacuo ( 110 ° c . ; 20 h ) in 4 m methanesulfonic acid containing 0 . 2 % 3 -( 2 - aminoethyl ) indole ( pierce ). amino acid analyses were performed on the hydrolyzates following derivatization with o - phthalidaldehyde reagent ( sigma chemical co .) using an automatic hplc system ( rainin instrument co .) fitted with a 100 × 4 . 6 mm , 3 μm c18 axial compression column with integral guard column ( microsorb aaanalysis ™, type o ; rainin instrument co .) the derivatized primary amino acids were eluted using a binary gradient of buffer a ; 0 . 10 m sodium acetate containing 4 . 5 % v / v methanol and 0 . 5 % v / v tetrahydrofuran at ph 7 . 2 and buffer b ; methanol . the gradient sequence ; 0 % a at 0 min ; 35 % a at 16 . 5 min ; 90 % a at 30 min and 90 % a at 33 min was used with a flow rate of 1 . 0 ml min − 1 at ambient temperature . eluent was monitored at 340 nm and integrated by the dynamax hplc method manager ( rainin ). standard retention times were as follows : asp , 6 . 6 min ; arg , 19 . 9 min ; trp , 25 . 4 min and lys , 29 . 5 min . each peptide of table i produced the expected analytical results for the primary amino acids . cysteine was not quantified . mass spectrometry . peptides were analyzed by matrix - assisted laser desorption / ionization time - of - flight mass spectrometry using a lasermat 2000 mass spectrometer ( thermal bioanalysis , san jose , calif .) using α - cyano - 4 - hydroxycinnamic acid as the matrix with substance p ( 1348 . 7 da ) as an internal standard . in each case , the spectra consisted of a major m - h ion peak for the internal standard , the expected analyte m - h peak , and a few peaks associated with the matrix (& lt ; 500 da ). mass values so derived for certain representative compounds of the instant invention are detailed in table 1 . srif analogue inhibition of gh release . anterior pituitaries from adult male rats were collected and dispersed by a previously described trypsin / dnase method . ( murphy , w . a . ; taylor , j . ; moreau , j .- p . and coy , d . h ., peptide res . 1989 , 2 , 128 - 132 .) the dispersed cells were diluted with sterile - filtered dulbecco &# 39 ; s modified eagle medium ( mem , gibco laboratories , grand island , n . y . ), which was supplemented with 2 . 5 % fetal calf serum ( gibco ), 3 % horse serum ( gibco ), 10 % fresh rat serum ( stored on ice for no longer than 1 h ) from the pituitary donors , 1 % mem nonessential amino acids ( gibco ), gentamycin ( 10 ng ml − 1 ; sigma ) and nystatin ( 10 , 000 u ml − 1 ; gibco ). the cells were randomly plated at a density of approximately 200 , 000 cells / well ( costar cluster 24 ; rochester scientific co ., rochester , n . y .). the plated cells were maintained in the above dulbecco &# 39 ; s medium in a humidified atmosphere of 95 % air / 5 % co 2 at 37 ° c . for 4 - 5 days . in preparation for a hormone challenge , the cells were washed with medium 199 ( gibco , 3 × 1 ml ). each dose of a compound of this invention was tested in triplicate wells in a total volume of 1 ml medium 199 containing 1 % bsa ( fraction v ; sigma chemical co .). all wells contained growth hormone releasing hormone ( 1 - 29 ) nh 2 ( ghrh ( 1 - 29 ) nh 2 ) ( 1 nm ). after incubation in an air / carbon dioxide atmosphere ( 95 / 5 %, 3 h at 37 ° c . ), the medium was removed and stored at − 20 ° c . until assayed for hormone content . growth hormone in media was measured by a standard double antibody radioimmunoassay ( ria ) using components generously supplied by dr . a . f . parlow at the national hormone and pituitary program ( nhhp ) torrance , calif . agonist ic 50 &# 39 ; s were calculated using sigmaplot ( jandel scientific , san rafael , calif .). values are expressed as the mean ic 50 ( nm )± sem from ( n ) separate dose - response curves . functional expression of the cloned human somatostatin receptors . the genomic clones containing the human somatostatin receptors ( hsstr - 1 to hsstr - 5 ) ( yamada , y ., et al . al ., proc . natl . acad . sci . usa . 1992 , 89 , 251 - 255 ; yasuda , k ., et al ., j . biol . chem . 1992 , 267 , 20422 - 20428 ; yamada , y ., et al ., mol . pharmacol . 1992 , 42 , 2136 - 2142 ; rohrer , l ., et al ., proc . natl . acad . sci . usa . 1993 , 90 , 4196 - 4200 .) were kindly provided by dr . graeme i . bell of the university of chicago . the hsstr - 1 , hsstr - 2 , hsstr - 3 , hsstr - 4 and hsstr - 5 cdnas were isolated as a 1 , 5 - kb psti - xmni fragment , 1 , 7 - kb bamhi - hindiii fragment , 2 , 0 - kb ncoi - hindiii fragment , 1 , 4 - kb nhei - ndei fragment , and a 1 , 2 - kb hindiii - xbai fragment , respectively , each containing the entire coding region of the full - length receptors . these fragments were independently subcloned into the corresponding restriction endonuclease sites in the mammalian expression vector pcmv5 , downstream from the human cytomegalovirus ( cmv ) promoter , to produce the expression plasmids pcmv5 / hsstr - 1 , pcmv5 / hsstr - 2 , pcmv5 / hsstr - 3 , pcmv5 / hsstr - 4 and pcmv5 / hsstr - 5 . for transfection into cho - k1 cells , a plasmid , prsv - neo ( american type culture collection , rockville , md . ), carrying the neomycin mammalian cell selectable marker was added . receptor expression and transfection . transfections were performed by the calcium phosphate method . cho - k1 cells were maintained in α - minimum essential medium ( α - mem ; gibco ) supplemented with 10 % fetal calf serum and transfected with each of the expression plasmids using calcium phosphate precipitation . clones that had inherited the expression plasmid were selected in α - mem supplemented with 500 μg ml − 1 of geneticin ( g418 ; gibco ). independent cho - k1 clones were picked by glass - ring cloning and expanded in culture in the selective media . membranes were prepared from the isolated clones and hsstr expression was initially assessed for binding with [ 125 i ] tyr 11 - srif and [ 125 i ] mk - 678 ( for sstr - 2 ). radioligand binding assays . cell membranes of the 5 cells types were obtained from homogenates ( polytron setting 6 , 15 sec ) of the corresponding cho - k1 cells , in ice - cold tris - hcl ( 50 mm ) and centrifuged ( 39000 g , 10 min × 2 ), with an intermediate resuspension in fresh buffer . the final pellets were resuspended in tris - hcl ( 10 mm ) for assay . aliquots of the membranes were incubated ( 30 min at 37 ° c .) with 0 . 05 nm [ 125 i ] tyr 11 - srif ( types 1 , 3 , 4 , 5 ) or [ 125 i ] mk - 678 ( type 2 ) in 50 nm hepes ( ph 7 . 4 ) containing bsa ( 10 mg ml − 1 ); mgcl 2 ( 5 mm ), trasylol ( 200 kiu ml − 1 ), bacitracin ( 0 . 02 mg ml − 1 ), and phenylmethanesulfonyl fluoride ( 0 . 02 mg ml − 1 ). the final assay volume was 0 . 3 ml and incubations were terminated by rapid filtration through gf / c filters pre - soaked in 0 . 3 % poly ( ethylenimine ) using a brandel rapid filtration module . each tube and filter was then washed with aliquots of cold buffer ( 3 × 5 ml ). specific binding is defined as the total radioligand bound minus that bound in the presence of 1 . 0 μm srif . the following total radioligand binding and non - specific binding ( nsb ) values were typically obtained with these assay systems : hsstr - 1 , 7000 cpm total versus 3500 cpm nsb ; hsstr - 2 , 9000 cpm total versus 1000 cpm nsb ; hsstr - 3 , 8000 cpm total versus 1000 cpm nsb ; hsstr - 4 , 6000 cpm total versus 3500 cpm nsb ; and hsstr - 5 , 7500 cpm total versus 3500 cpm nsb . the binding affinities are expressed as ki values ± sem ( nm ) for each of the five receptor subtypes . ki values derived for representative compounds of the instant invention are detailed in table 2 . molecular modeling . all molecular modeling was performed on a silicon graphics indigo 2 high impact 10000 computer , using sybyl 6 . 6 with the kollman all atom force field . the pdb files for the three solution nuclear magnetic resonance ( nmr ) structures of the initial compound sandostatin / octreotide ®; dphe 5 - c [ cys 6 - phe 7 - dtrp 8 - lys 9 - thr 10 - cys 11 ]- thr 12 - ol ( 1soc and 2soc ) were obtained from the pdb database . these structures were imported into sybyl6 . 6 and mutated to form the n - methylated compounds based on example 9 . the kollman partial atomic charges were loaded from the monomer dictionary . the structures were optimized by annealing the mutated residue and then by full energy minimization using the conjugate gradient algorithm to a final root mean square ( rms ) gradient of ≦ 0 . 01 kcal mol . å − 1 . a distance - dependent dielectric function was employed together with the default settings for all the other minimization options . examples 9 and 18 were alkylated at every residue by a solid phase procedure whilst being assembled on methylbenzhydrylamine resin . after the tert - butoxycarbonyl ( boc ) group was removed at the desired n - methylation site , the free amine of the resin bound peptide was protected using o - nitrobenzenesulfonyl chloride and collidine in dichloromethane . then the amide n — h of o - nitrobenzenesulfonamide was selectively deprotonated by the strong , hindered , non - ionic base mtbd and methylated using methyl p - nitrobenzenesulfonate in dmf . the methylated sulfonamide was deprotected by β - mercaptoethanol and dbu in dmf and this reaction was easily followed by the appearance of bright yellow color in the solution , indicating the removal of o - nitrobenzenesulfonyl group from the resin bound peptide . also , this deprotection was slower if the n - sulfonamide was not alkylated , thus capping the unalkylated peptide . the subsequent amino acid was coupled two times using tbtu / dipea instead of dic . the sequence ( o - nbs ) hn - cys 11 ( 4 - mez )- thr 12 ( obzl )-® could not be methylated using methyl o - nitrobenzenesulfonate . this problem was , however , circumvented by using dimethyl sulfate as a methylating agent instead of the bulky methyl o - nitrobenzenesulfonate . the binding affinities ( kd , nm ) of all srif analogues were determined using their concentration - dependent displacement of 125 i - radiolabeled peptide ligands from membranes isolated from cho cells transfected with the corresponding human somatostatin receptor . for reference , the binding affinities of srif - 14 and srif - 28 in the same system were used . srif - 28 displays particularly high affinity for type 5 receptors compared to srif - 14 . given the profound effect which the conformation and side - chain of the n - terminal amino acid has on the biological activities of this type of analogue , two series of base structure ( compounds 9 and 18 ) were used for the present study — one containing a d phe ( analogue 9 ) and the other a tyr residue ( analogue 18 ) to give a total of 16 n - methylated analogues , the structures and physicochemical characteristics of which are given in table 1 . the compounds of the present invention were synthesized as described above and / or as described in the various references cited herein . it is to be understood that while the invention has been described in conjunction with the detailed description thereof , that the foregoing description is intended to illustrate and not to limit the scope of the invention . other aspects , advantages , and modifications are within the claims . also , the contents of each references cited herein is incorporated by reference in its entirety .
claimed are a series of somatostatin agonists and uses thereof , according to formula , a 1 - cyclo - a 5 - y 1 , wherein a 1 , a 2 , a 3 , a 4 , a 5 and y 1 are as defined in specification provided that the amine nitrogen of at least one peptide bond is substituted with a methyl group or pharmaceutically acceptable salts thereof .