J . Med. Chem. 1995,38,1015-1021
1015
Ketomethylene and (Cyanomethy1ene)aminoPseudopeptide Analogues of the C-Terminal Hexapeptide of Neurotensin Rosario Gonzalez-Mufiiz,*J M. Teresa Garcia-Lopez,+Isabel Gomez-Monterrey,t Rosario Herranz,? M. Luisa Jimeno,+M. Luisa Suarez-Gea,? Nils L. Johansen,* Kjeld Madsen,* Henning Th~gersenPand Peter Suzdakt Instituto de Quimica Mkdica (CSIC), J u a n de la Cierva 3, E-28006 Madrid, Spain, and C N S Division, Novo Nordisk, Novo Nordisk Park, DK-2760 Maaloev, Denmark Received October 18, 1994@
A series of pseudopeptide analogues of the C-terminal hexapeptide of neurotensin (NT8-13), namely [Tyr11Y[COCH21Phe121-,[Ile12Y[COCH21Phe131-,and [Tyr11Y[CH(CN)NHlIle121NT8-13 with different stereochemistries, has been synthesized and evaluated for its potency in displacing labeled NT from rat cortex membranes. Ketomethylene pseudohexapeptides were prepared from the corresponding Boc-protected ketomethylene dipeptide derivatives, previously formed, using different solid phase synthesis (SPS) conditions, while (cyanomethy1ene)amino analogues were directly prepared by SPS using Fmoc strategy. H-Arg-Arg-Pro-TyrY[COCH21Phe-Leu-OH was nearly as potent as NT8-13 and [Phel2lNT8-l3 in binding to the receptor. Comparison of the affinities for the pseudohexapeptides, here reported, with those of the Y[CHzNH] analogues indicates the importance of the CO group in the amide or surrogate linkage at 11-12 and 12-13 positions in the receptor binding process. substitute.15-17 Additionally, in this new peptide bond surrogate, the cyano group keeps H-bonding acceptor Neurotensin (NT) is a biologically active peptide properties while the new asymmetric center could largely distributed in the central nervous system and impart higher backbone rigidity than the reduced pepsome regions of the digestive tract in various mammals, tide bond. including man.1-3 It has been shown that this peptide In the present article, we report the preparation of a produces hypotension, increases vascular permeability, series of NT8-13 analogues, 12-14, incorporating Ypossesses antinociceptive properties, and elicits anti[COCH21 and Y[CH(CN)NHl surrogates at 11-12 and psychotic-like effects in animal test^.^,^ The C-terminal 12-13 positions and their ability to inhibit the binding hexapeptide of NT, H-Arg-Arg-Pro-Tyr-Ile-Leu-OH of 3H-labeledNT to rat cortex membranes. The results (NT8-13), contains all the necessary information to of the binding assays are compared with those of the trigger the biological response of NT.536 corresponding hexapeptides and reduced peptide bond In an attempt to provide resistance to peptidases, a analogues. systematic replacement of each peptide bond in NT8-13 with the reduced Y[CHzNH] isostere was H-hg-hg-Pro-TyrY[COCH,lPhe-Leu-OH (12) Except for the [ArgsY[CH2NHIArgSlNT8-13 derivative, these replacements resulted in a decrease in affinity for H-Arg-Arg-Pro-Tyr-I1eY[COCH,lPhe-OH(13) NT receptors, particularly marked in pseudohexapeptides incorporating the reduced bond between the 11H-Arg-Arg-Pro-TyrY[CH( CN)NH]Ile-Leu-OH (14) 12 and 12-13 residues. Similar results were found when the Ile12-Leu13 peptide bond was replaced with Results and Discussion the retro-amide isostere.1° Chemistry. Considering that in our previous bindNow, in order to further investigate the functional role ing assays the substitution of Ile12 or Leu13 by a Phe of the Tyrl1-Ilel2 and Ile12-Leu13 amide bonds in residue did not modify the activity of NT8-13, and in NT8-13, we have selected the ketomethylene [COCH21 order to facilitate the synthetic pathway, the ketomethand (cyanomethy1ene)amino [CH(CN)NHl groups as ylene pseudodipeptides to be incorporated into the appropriate surrogates for this purpose. Thus, similarly NT8-13 sequence bear a Phe side chain at the Cto the introduction of the Y[CH2NH] bond into peptides, terminus. Protected ketomethylene derivatives Bocthe popular COCH2 group, widely used for the preparaTyr(2,6-di-Cl-Bzl)-Y[C0CH~l(R,S)Phe-OH (9) and Boction of metabolically stable neuropeptide analoguesll (10) were prepared following IleY[COCH21(R,S)Phe-OH and enzyme inhibitors,12J3increases the conformational a similar method to that previously reported for the freedom.14 In contrast, the hydrogen bond properties preparation of these peptide bond surrogates (Scheme of both isosteres are opposite (donor or acceptor). l).18J9 Thus, the y-keto diesters 3 and 4, prepared by Concerning the recently reported CH(CN)NH group, reaction of the corresponding chloromethyl ketones 1 semiempirical quantum mechanic calculations have and 2 with the monosodium salt of dibenzyl malonate, indicated that, due to its electronic properties, it could were alkylated with benzyl bromide, using sodium be a better mimic of the amide bond than the CHzNH hydride as base, to provide the 2-disubstituted derivatives 5 and 6, respectively. Hydrogenolysis of comInstituto de Quimica MBdica. 5 and 6, followed by decarboxylation of the pounds CNS Division, Novo Nordisk. resulting malonic acid derivatives 7 and 8, afforded Abstract published in Advance ACS Abstracts, February 15,1995.
Introduction
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0022-262319511838-1015$09.00/0
0 1995 American Chemical Society
Gonzalez-Miiniz et al.
1016 Journal of Medicinal Chemistry, 1995, Vol. 38, No. 6
Scheme 1
Table 1. Epimerization a t Ile Ca of Ketomethylene Pseudopeptides 10a and 13a under Basic Conditions compound (%) conditions
R
1
2- NaCH(C02Bzl)2
formation of Cs salt, 18 h in DMF a t 50 "C DMAP (0.1 equiv) DCM, 18 h 10%DIEA, DMF, 30 min 20% piperidine, DMF, 2.5 h a
10a >45"
