Peptidomimetics in Drug Design

Recent Advances in the Field of Amino Acid-Conjugated Aminoferrocenes-A Personal Perspective

The development of turn-based inhibitors of protein-protein interactions has attracted considerable attention in medicinal chemistry. Our group has synthesized a series of peptides derived from an amino-functionalized ferrocene to investigate their potential to mimic protein turn structures. Detailed DFT and spectroscopic studies (IR, NMR, CD) have shown that, for peptides, the backbone chirality and bulkiness of the amino acid side chains determine the hydrogen-bond pattern, allowing tuning of the size of the preferred hydrogen-bonded ring in turn-folded structures. However, their biological potential is more dependent on their lipophilicity. In addition, our pioneering work on the chiroptical properties of aminoferrocene-containing peptides enables the correlation of their geometry with the sign of the CD signal in the absorption region of the ferrocene chromophore. These studies have opened up the possibility of using aminoferrocene and its derivatives as chirooptical probes for the determination of various chirality elements, such as the central chirality of amino acids and the helicity of peptide sequences.

Non-Canonical Amino Acids as Building Blocks for Peptidomimetics: Structure, Function, and Applications

This review provides a fresh overview of non-canonical amino acids and their applications in the design of peptidomimetics. Non-canonical amino acids appear widely distributed in nature and are known to enhance the stability of specific secondary structures and/or biological function. Contrary to the ubiquitous DNA-encoded amino acids, the structure and function of these residues are not fully understood. Here, results from experimental and molecular modelling approaches are gathered to classify several classes of non-canonical amino acids according to their ability to induce specific secondary structures yielding different biological functions and improved stability. Regarding side-chain modifications, symmetrical and asymmetrical α,α-dialkyl glycines, Cα to Cα cyclized amino acids, proline analogues, β-substituted amino acids, and α,β-dehydro amino acids are some of the non-canonical representatives addressed. Backbone modifications were also examined, especially those that result in retro-inverso peptidomimetics and depsipeptides. All this knowledge has an important application in the field of peptidomimetics, which is in continuous progress and promises to deliver new biologically active molecules and new materials in the near future.

Insect kinin mimics act as potential control agents for aphids: Structural modifications of Trp4

Insect kinins are endogenous, biologically active peptides with various physiological functions. The use of insect kinins in plant protection is being evaluated by many groups. Some kinins have been chosen as lead compounds for pest control. We previously reported an insect kinin mimic IV-3 that had insecticidal activity. And by introducing a strong electron withdrawing group (-CF₃ ) on the benzene ring (Phe² ), we discovered a compound, L₇ , with better activity than lead IV-3. In this work, taking L₇ as the lead compound, we designed and synthesized 13 compounds to evaluate the influence of position 4 (Trp⁴ ) of insect kinin on insecticidal activity, by replacing the H atom on tryptophan with -CH₃ and -Cl or substituting the indole ring of tryptophan with the benzene, naphthalene, pyridine, imidazole, cyclohexane, and alkyl carboxamides. The aphid bioassay results showed that the compounds M₁ , M₃ , and M₅ were more active than the positive control, pymetrozine. Especially, replacing the side chain by an indole ring with 4-Cl substitution (M₁ , LC₅₀  = 0.0029 mmol/L) increased the aphicidal activity. The structure-activity relationships (SARs) indicated that the side chain benzene ring at this position may be important to the aphicidal activity. In addition, the toxicity prediction by Toxtree, and the toxicity experiments on Apis mellifera suggested that M₁ was no toxicity risk on a non-target organism. It could be used as a selective and bee-friendly insecticide to control aphids.

Synthesis, structural characterization, and evaluation of new peptidomimetic Schiff bases as potential antithrombotic agents

New Schiff bases functionalized with amide and phenolic groups synthesized by the condensation of 2-hydroxybenzaldehyde and 2-hydroxyacetophenone with amino acid amides which in turn were prepared in two steps from N-Boc-amino acids and homoveraltrylamine through intermediate compounds N-Boc-amino acids amides. The compounds were characterized by elemental analysis, FT-IR, UV–Vis, and NMR spectroscopy. The crystal structures of three Schiff bases were determined by single crystal X-ray diffraction. There exists O–H\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\cdots $$\end{document}⋯N, N–H\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\cdots $$\end{document}⋯O, and C–H\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\cdots $$\end{document}⋯O types of hydrogen bonds and C–H\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\cdots\uppi $$\end{document}⋯π secondary bonding interactions in these crystalline solids. The Schiff bases have been screened for anticoagulant and antiplatelet aggregation activities. All the compounds showed procoagulant activity which shortens the clotting time of citrated human plasma in both platelet-rich plasma and platelet-poor plasma except the derivatives of L-methionine which showed anticoagulant activity by prolonging the clotting time. In addition, the compounds derived from benzyl cysteine and phenylalanine showed adenosine diphosphate induced antiplatelet aggregation activity, whereas others did not show any role. Moreover, all these compounds revealed non-hemolytic activity with red blood cells.

A novel bee-friendly peptidomimetic insecticide: Synthesis, aphicidal activity and 3D-QSAR study of insect kinin analogs at Phe2 modification

BACKGROUND

As one of the most abundant and destructive pests in agriculture, aphids cause significant damage to crops due to their sap-taking and as virus vectors. Chemical insecticides are the most effective method to control aphids, but they bring insecticide resistance problems and harm nontarget organisms, especially bees, therefore the search for novel eco-friendly aphid control agents with low bee toxicity is urgent. Insect kinins are a class of small neuropeptides that control important functions in insects. In our previous study, we found insect kinin analog IV-3 has good aphicidal activity and the location of the aromatic ring on the side chain of Phe² is the key to the formation of the β-turn resulting in the biological activity of insect kinin analogs. However, there are few studies on insect kinin Phe² substitution and modification, and its structure-activity relationship is still unclear.

RESULTS

In this project, 44 insect kinin analogs with the Phe² modification, replacing it with different natural or unnatural amino acids, were designed and synthesized based on the lead IV-3 to explore the role of the Phe² residues. Bioassays with soybean aphids of Aphis glycines indicated that nine analogs have better aphicidal activity than the lead IV-3. In particular, compound L₂₅ exhibits excellent aphicidal activity (LC₅₀  = 0.0047 mmol L^-1 ) and has low toxicity to bees. Furthermore, a reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) was established to produce a helpful clue that introducing hydrophobic groups away from the backbone chain is beneficial to improve aphicidal activity.

CONCLUSION

The residue Phe² of insect kinin analogs is the key position and has a significant impact on the activity. L₂₅ has a high toxicity for aphids, while a low toxicity to bees, and therefore can be considered as a lead compound to develop new biosafe aphid control agents. Finally, we provide a useful 3D-QSAR model as theoretical guidance for further structural optimization. © 2022 Society of Chemical Industry.

Synthesis, aphicidal activity and conformation of novel insect kinin analogues as potential eco-friendly insecticides

BACKGROUND

The discovery of ecofriendly insecticides through a new strategy for aphid control is important because of the substantial resistance and unexpected eco-toxicity to honeybees caused by traditional insecticides. The insect kinins, a class of multifunctional insect neuropeptides, are considered for potential application in pest control. In our previous work we developed several series of insect kinin analogues and found a promising lead II-1 with good aphicidal activity. To seek further eco-friendly aphicides, the optimization of II-1 is carried out in this study.

RESULTS

Fifteen novel Yaa³ modified analogues based on the lead II-1 were synthesized. The aphicidal tests indicated that IV-3, IV-5 and IV-10 exhibited significant activity against the soybean aphid Aphis glycines with LC₅₀ values of 0.0029, 0.0072 and 0.0086 mmol L^-1 , respectively, higher than that of lead II-1 and the commercial Pymetrozine. The molecular modeling results showed that analogues II-1, IV-3, IV-5, IV-7 and IV-10 formed a β-turn-like conformation, while the conformation of analogues IV-1, IV-2 and IV-9 seemed to be linear. Some structural elements favorable for the activity were proposed based on the conformation-activity relationship of the analogues.

CONCLUSION

Insect kinin analogues derived from lead II-1 by modifying the hydrolysis site Yaa³ with natural, sterically hindered α- and β-amino acids showed great potential as eco-friendly insecticides. Inspiringly, the most active analogue IV-3 can be a candidate for further development. The β-turn-like conformation and the orientation of the aromatic rings of the side chain of Phe² and Trp⁴ may be critical factors beneficial to activity. © 2019 Society of Chemical Industry.

H-Bond Surrogate-Stabilized Shortest Single-Turn α-Helices: sp2 Constraints and Residue Preferences for the Highest α-Helicities

Short α-helical sequences of proteins fail to maintain their native conformation when taken out of their protein context. Several covalent constraints have been designed, including the covalent H-bond surrogate (HBS)-where a peptide backbone i + 4 → i H-bond is replaced by a covalent surrogate-to nucleate α-helix in short sequences (>7 < 15 amino acids). But constraining the shortest sequences (four amino acids) into a single α-helical turn is still a significant challenge. Here, we introduce an HBS model that can be placed in unstructured tetrapeptides without excising any of its residues, and that biases them predominantly into remarkably stable single α-helical turns in varying solvents, pH values, and temperatures. Circular dichroism (CD), Fourier transform infrared (FT-IR) absorption, one-dimensional (1D)-NMR, two-dimensional (2D)-NMR spectral and computational analyses of the HBS-constrained tetrapeptide analogues reveal that (a) the number of sp² atoms in the HBS-constrained backbone influences their predominance and rigidity in the α-helical conformation; and (b) residue preferences at the unnatural HBS-constrained positions influence their α-helicities, with Moc[GFA]G-OMe (1a) showing the highest known α-helicity (θ_n→π*MRE ∼-25.3 × 10³ deg cm² dmol^-1 at 228 nm) for a single α-helical turn. Current findings benefit chemical biological applications desiring predictable access to single α-helical turns in tetrapeptides.

Preparation of a radiolabeled GnRH-I analogue derivative with 111 In as a new anti-proliferative agent

The new GnRH-Ιanalogue developed in this paper was based on the D-Trp⁶ -GnRH-Ι-scaffold, and its potency was increased by the replacement Gly-NH₂ by NH-NH₂ binding to the Gly at position 10. Triptorelin-Hydrazide analogue was synthesized using solid phase. For ¹¹¹ In labeling, synthesized peptide was followed by conjugation with DOTA using pSCN-Bn-DOTA. The conjugated Triptorelin-Hydrazide was labeled with 500-550 MBq of ¹¹¹ In-chloride (in 0.2 M HCl). At optimized conditions after labeling, radio-chromatography showed radiochemical purity of approximately equal to 98% (RTLC) and greater than 95% (HPLC). The serum stability of the tracer was determined up to 24 hr. Binding affinities of Triptorelin-Hydrazide analogue were determined in a binding assay for both human and rat GnRH receptors. For in vivo studies, ¹¹¹ In-peptide was injected intravenously via the tail vein into rats and significant ovaries uptake consist with reported GnRH receptor mappings. In vitro radioligand binding assays performed with GnRHR-expressing human cell lines using ¹²⁵ I-Triptorelin as the standard radioligand. The quantities of internalization efficiency and receptor affinity of the new radioligand were IC₅₀  = 0.20 ± 0.04 nM vs 0.13 ± 0.08 nM for Triptorelin and internalization: 3.5 ± 0.9% at 1 hr and 12.8 ± 1.8% at 4 hr of the internal reference.

Design, synthesis and aphicidal activity of N-terminal modified insect kinin analogs

The insect kinins are a class of multifunctional insect neuropeptides present in a diverse variety of insects. Insect kinin analogs showed multiple bioactivities, especially, the aphicidal activity. To find a biostable and bioactive insecticide candidate with simplified structure, a series of N-terminal modified insect kinin analogs was designed and synthesized based on the lead compound [Aib]-Phe-Phe-[Aib]-Trp-Gly-NH2. Their aphicidal activity against the soybean aphid Aphis glycines was evaluated. The results showed that all the analogs maintained the aphicidal activity. In particular, the aphicidal activity of the pentapeptide analog X Phe-Phe-[Aib]-Trp-Gly-NH2 (LC50=0.045mmol/L) was similar to the lead compound (LC50=0.048mmol/L). This indicated that the N-terminal protective group may not play an important role in the activity and the analogs structure could be simplified to pentapeptide analogs while retaining good aphicidal activity. The core pentapeptide analog X can be used as the lead compound for further chemical modifications to discover potential insecticides.

Eco-Friendly Insecticide Discovery via Peptidomimetics: Design, Synthesis, and Aphicidal Activity of Novel Insect Kinin Analogues

Insect kinin neuropeptides are pleiotropic peptides that are involved in the regulation of hindgut contraction, diuresis, and digestive enzyme release. They share a common C-terminal pentapeptide sequence of Phe(1)-Xaa(2)-Yaa(3)-Trp(4)-Gly(5)-NH2 (where Xaa(2) = His, Asn, Phe, Ser, or Tyr; Yaa(3) = Pro, Ser, or Ala). Recently, the aphicidal activity of insect kinin analogues has attracted the attention of researchers. Our previous work demonstrated that the sequence-simplified insect kinin pentapeptide analogue Phe-Phe-[Aib]-Trp-Gly-NH2 could retain good aphicidal activity and be the lead compound for the further discovery of eco-friendly insecticides which encompassed a broad array of biochemicals derived from micro-organisms and other natural sources. Using the peptidomimetics strategy, we chose Phe-Phe-[Aib]-Trp-Gly-NH2 as the lead compound, and we designed and synthesized three series, including 31 novel insect kinin analogues. The aphicidal activity of the new analogues against soybean aphid was determined. The results showed that all of the analogues exhibited aphicidal activity. Of particular interest was the analogue II-1, which exhibited improved aphicidal activity with an LC50 of 0.019 mmol/L compared with the lead compound (LC50 = 0.045 mmol/L) or the commercial insecticide pymetrozine (LC50 = 0.034 mmol/L). This suggests that the analogue II-1 could be used as a new lead for the discovery of potential eco-friendly insecticides.

Effect of sequence and stereochemistry reversal on p53 peptide mimicry

Peptidomimetics effective in modulating protein-protein interactions and resistant to proteolysis have potential in therapeutic applications. An appealing yet underperforming peptidomimetic strategy is to employ D-amino acids and reversed sequences to mimic a lead peptide conformation, either separately or as the combined retro-inverso peptide. In this work, we examine the conformations of inverse, reverse and retro-inverso peptides of p53(15-29) using implicit solvent molecular dynamics simulation and circular dichroism spectroscopy. In order to obtain converged ensembles for the peptides, we find enhanced sampling is required via the replica exchange molecular dynamics method. From these replica exchange simulations, the D-peptide analogues of p53(15-29) result in a predominantly left-handed helical conformation. When the parent sequence is reversed sequence as either the L-peptide and D-peptide, these peptides display a greater helical propensity, feature reflected by NMR and CD studies in TFE/water solvent. The simulations also indicate that, while approximately similar orientations of the side-chains are possible by the peptide analogues, their ability to mimic the parent peptide is severely compromised by backbone orientation (for D-amino acids) and side-chain orientation (for reversed sequences). A retro-inverso peptide is disadvantaged as a mimic in both aspects, and further chemical modification is required to enable this concept to be used fruitfully in peptidomimetic design. The replica exchange molecular simulation approach adopted here, with its ability to provide detailed conformational insights into modified peptides, has potential as a tool to guide structure-based design of new improved peptidomimetics.

Peptidomimetics in the discovery of new insect growth regulators: studies on the structure-activity relationships of the core pentapeptide region of allatostatins

Cockroach-type allatostatins (ASTs) were discovered in cockroaches through their capacity to inhibit the production of juvenile hormone by the corpora allata (CA). ASTs were considered as potential insect growth regulator (IGR) candidates, but several disadvantages, including the absence of the effect in vivo and rapid degradation in vivo, precluded their application in pest management. The CA were selected as the target, and the core pentapeptide region (YDFGL) was chosen as the lead sequence in the search for new IGRs based on the allatostatins. We designed and synthesized 24 analogues, which mimicked each amino acid of the core region, to determine structure-activity relationships and the possibility of shortening the ASTs in the core region while retaining activity. The results suggest that the sequence FGLa is more important than Y/FX because Y/FX mimics show strong effects in vitro and in vivo. In particular, compound I3 was synthesized by substitution of Y/FX with 6-phenylhexnoic acid and exhibits higher activity in vitro than the complete core region. Furthermore, compound I3 has a clear effect in vivo on juvenile hormone (JH) biosynthesis of Diploptera punctata females, providing a possible application for cockroach management. On the basis of the structure-activity relationship of pentapeptide analogues, a general structure of potential potent AST analogues is proposed here. A new approach using peptidomimetics in the discovery of IGRs is demonstrated in our study.

Targeting PKC-β II by Peptides and Peptidomimetics Derived from RACK 1: An In Silico Approach

Diabetes causes contractile myocardial dysfunction through accelerated atherosclerosis and hypertension, termed Diabetic Cardiomyopathy. Experimental results reveals liaison between cardiovascular disease and diabetic complications. Protein kinase C (PKC), a heterogeneous family of phospholipid dependent kinases was found to be specifically involved in diabetic complications, of which PKC-β II isoform played a significant role in induction of this fatal disease. Members of PKC family share high degree of similarity in both structure and functions, which has given rise to specificity related issues. In the present study, we have designed peptides and peptidomimetics based on RACK 1 (Receptor for Activated C Kinases) region, as this protein increases the substrate phosphorylation and stabilizes the activated form of PKC-β II. RACK 1 being specific for PKC-β II could resolve the specificity issue and also peptides and peptidomimetics, being conformationally restrained structures offers potential advantages of being used as drug molecules over organic molecules. This study has provided useful insights that may contribute to the development of molecules which may be useful in the treatment of diabetic complications.

An efficient synthesis of a rationally designed 1,5 disubstituted imidazole AT(1) angiotensin II receptor antagonist: reorientation of imidazole pharmacophore groups in losartan reserves high receptor affinity and confirms docking studies

A new 1,5 disubstituted imidazole AT(1) Angiotensin II (AII) receptor antagonist related to losartan with reversion of butyl and hydroxymethyl groups at the 2-, 5-positions of the imidazole ring was synthesized and evaluated for its antagonist activity (V8). In vitro results indicated that the reorientation of butyl and hydroxymethyl groups on the imidazole template of losartan retained high binding affinity to the AT(1) receptor concluding that the spacing of the substituents at the 2,5- positions is of primary importance. The docking studies are confirmed by binding assay results which clearly show a comparable binding score of the designed compound V8 with that of the prototype losartan. An efficient, regioselective and cost effective synthesis renders the new compound as an attractive candidate for advanced toxicological evaluation and a drug against hypertension.

Synthesis, binding studies and in vivo biological evaluation of novel non-peptide antihypertensive analogues

AT(1) antagonists (SARTANs) constitute the last generation of drugs for the treatment of hypertension, designed and synthesized to mimic the C-terminal segment of the vasoconstrictive hormone angiotensin II (AngII). They exert their action by blocking the binding of AngII on the AT(1) receptor. Up to date eight AT(1) antagonists have been approved for the regulation of high blood pressure. Although these molecules share common structural features and are designed to act under the same mechanism, they have differences in their pharmacological profiles and antihypertensive efficacy. Thus, there is still a need for novel analogues with better pharmacological and financial profiles. An example of a novel synthetic non peptide AT(1) antagonist which devoids the classical template of SARTANs is MM1. In vivo studies showed that MMK molecules, which fall in the same class of MM1, had a significant antihypertensive (40-80% compared to the drug losartan) activity. However, in vitro affinity studies showed that losartan has considerably higher affinity. The theoretical docking studies showed that MM1 acts on the same site of the receptor as losartan. They exert hydrophobic interactions with amino acid Val108 of the third helix of the AT(1) receptor and other hydrophobic amino acids in spatial vicinity. In addition, losartan favours multiple hydrogen bondings between its tetrazole group with Lys199. These additional interactions may in part explain its higher in vitro binding affinity.

Old Molecules for New Receptors: Trp(Nps) Dipeptide Derivatives as Vanilloid TRPV1 Channel Blockers

The transient receptor potential vanilloid member 1 (TRPV1), an integrator of multiple pain-producing stimuli, is regarded nowadays as an important biological target for the discovery of novel analgesics. Here, we describe the first experimental evidence for the behavior of an old family of analgesic dipeptides, namely Xaa-Trp(Nps) and Trp(Nps)-Xaa (Xaa=Lys, Arg) derivatives, as potent TRPV1 channel blockers. We also report the synthesis and biological investigation of a series of new conformationally restricted Trp(Nps)-dipeptide derivatives with improved TRPV1/NMDA selectivity. Compound 15 b, which incorporates an N-terminal 2S-azetidine-derived Arg residue, was the most selective compound in this series. Collectively, a new family of TRPV1 channel blockers emerged from our results, although further modifications are required to fine-tune the potency/selectivity/toxicity balance.

N-alkylated dipeptide amides and related structures as imitations of the melanocortins' active core

Thirty-three low molecular mass structures combining both peptide and peptoid features were prepared and tested on human melanocortin receptors MC1,3-5R. Most of them displayed low micromolar activity with preference for diamines, guanidino and 2-naphthyl derivatives compared to monoacetylated, amino and 3-indolyl counterparts. Some contained L- or D-histidine residues, but the change did not influence affinity. QSAR modelling yielded excellent models for the MC3-5 receptors explaining R2Y=0.89-0.91 and predicting Q2=0.77-0.80 of the affinity variations. One compound displayed MC1R selectivity (13-fold and more). An NMR study of showed that it exists as a mixture of four rotamers at its tertiary amide bonds. Comparisons with earlier data for melanocortin core tetrapeptide analogues indicate that the novel peptide-peptoids interact with the melanocortin receptors in a different way.

Design, Synthesis and Evaluation of a PLG Tripeptidomimetic Based on a Pyridine Scaffold

A 2,3,4-substituted pyridine derivative has been identified as a potential tripeptidomimetic scaffold. The design of the scaffold was based on conformational and electrostatic comparisons with a natural tripeptide. The scaffold has been used in the synthesis of a Pro-Leu-Gly-NH2 (PLG) mimetic. The different substituents in the 2-, 3-, and 4-positions of the pyridine ring were introduced via an aromatic nucleophilic substitution reaction, a "halogen-dancing" reaction, and a Grignard coupling of a Boc-protected amino aldehyde, respectively. The synthetic route involves eight steps and provides the mimetic in 20% overall yield. The pyridine based PLG-mimetic was evaluated for its ability to enhance the maximum response of the dopamine agonist N-propylapomorphine (NPA) at human D2 receptors using a cell based assay (the R-SAT assay). The dose-response curve of the mimetic was found to exhibit a down-turn phase, similar to that of PLG. In addition, the mimetic was more potent than PLG to enhance the NPA response; the maximum response was found to be 146% at 10 nM concentration, as compared to 115% for PLG at the same concentration. Interestingly, conformational analysis by molecular modeling showed that the pyridine mimetic cannot adopt a type II beta-turn conformation that previously has been suggested to be the bioactive conformation of PLG.

Conformationally tailored N-[(2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl)carbonyl]proline templates as molecular tools for the design of peptidomimetics. Design and synthesis of fibrinogen receptor antagonists

The proline peptide bond was shown by 2D proton NMR studies to exist exclusively in the trans conformation in benzyl (2S)-1-[[(2S)-2-methyl-6-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl]-2-pyrrolidinecarboxylate [(S,S)-11], benzyl (2S)-1-[[(2S)-2-methyl-7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl]-2-pyrrolidinecarboxylate [(S,S)-9], and in the corresponding 6-amino and 7-amino carboxylic acids (S,S)-3 and (S,S)-4. On the other hand, the diastereomers (R,S)-11 and (R,S)-9 containing an (R)[2-methyl-6/7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl moiety, and the diastereoisomers (R,S)-3 and (R,S)-4 incorporating an (R)[6/7-amino-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl moiety were found to exist as equilibria of trans(63-83%) and cis(17-37%) isomers. These conformationally defined templates were applied in the construction of RGD mimetics possessing antagonistic activity at the platelet fibrinogen receptor.

Synthesis of GDP-5-thiosugars and their use as glycosyl donor substrates for glycosyltransferases

Two thiopyranoside analogues of GDP-sugars, GDP-5-thio-d-mannose (14) and GDP-5-thio-l-fucose (15), were synthesized. The syntheses included the phosphorylations of tetra-O-acetyl-5-thio-d-mannosyl bromide (4) and tri-O-benzoyl-l-fucosyl bromide (6) with silver dibenzyl phosphate, deprotection of the phosphate groups, and condensation of the deprotected phosphates with GMP-imidazolidate (13) in the presence of MgCl(2). These GDP-sugar analogues were found to be donor substrates for alpha(1,2)mannosyltransferase and alpha(1,3)fucosyltransferase, affording a 5-thiomannose-containing disaccharide (18) and a 5-thiofucose-containing trisaccharide (21), respectively. The conformation of the disaccharide analogue 18 was similar to that of its native counterpart by ROESY. These findings for GDP-5-thiosugars together with previous demonstrations of enzymatic transfer from UDP-5-thiosugars will allow the production of panels of oligosaccharide analogues with hydrolase-resistant properties.

Diastereoselective synthesis and estimation of the conformational flexibility of 6-oxoperhydropyridazine-3-carboxylic acid derivatives

alpha,beta-Didehydroglutamates have been diastereoselectively transformed into 6-oxoperhydropyridazine-3-carboxylic acid derivatives (OPCAs), which constitute a new class of cyclic amino acid derivatives. Acylation at N-1 renders dipeptides which show considerable conformational rigidity. Semiempirical calculations suggest that OPCAs might force peptide turns with different amplitudes depending on the substitution pattern and relative stereochemistry of the substituents of the pyridazinone ring.

Targets of drug action

This article considers early work from the author's laboratory on muscarinic receptor specificity, subtypes, and conformational variability, with the use of nuclear magnetic resonance in pharmacology and the conformational variants of dihydrofolate reductase and general questions of receptors. It also considers some current approaches to drug development and receptor function, particularly as influenced by increasing knowledge of three-dimensional structure of receptors.

Chemoenzymatic Synthesis of Both Enantiomers of cis-6-(Hydroxymethyl)- and cis,cis-4-Hydroxy-6-(hydroxymethyl)pipecolic Acids

Both enantiomers of cis-6-(hydroxymethyl)- and cis,cis-4-hydroxy-6-(hydroxymethyl)pipecolic acids, piperidine-based nonproteinogenic amino acids, have been synthesized from starting materials obtained from enzymatic desymmetrizations.