Solid phase synthesis of oligomeric guanidiniums

Silver acetate-catalyzed synthesis of cyclic sulfonyl guanidine with exocyclic double bond

An efficient protocol for the synthesis of cyclic guanidine with exocyclic double bond has been developed. The synthesis has been achieved via intramolecular hydroamination of an intermediate propargyl guanidine by using silver acetate as catalyst in the presence of acetic acid. The reaction proceeds via the formation of acyclic propargyl guanidine in a one-pot reaction of N,N-dibromoarylsulfonamides, isonitriles, and propargylamine in the presence of K2CO3. In the second stage of the synthesis, the acyclic guanidine selectively undergoes 5-exo-dig cyclization in the presence of silver acetate and acetic acid to produce the five-membered cyclic guanidine framework having an exocyclic double bond as the constituent part. Short reaction time, wide substrate scope with good to high yields, and good functional group tolerance are the remarkable achievement of the present protocol.

Synthesis of Novel Arginine Building Blocks with Increased Lipophilicity Compatible with Solid-Phase Peptide Synthesis

Arginine, due to the guanidine moiety, increases peptides' hydrophilicity and enables interactions with charged molecules, but at the same time, its presence in a peptide chain might reduce its permeability through biological membranes. This might be resolved by temporary coverage of the peptide charge by lipophilic, enzyme-sensitive alkoxycarbonyl groups. Unfortunately, such a modification of a guanidine moiety has not been reported to date and turned out to be challenging. Here, we present a new, optimized strategy to obtain arginine building blocks with increased lipophilicity that were successfully utilized in the solid-phase peptide synthesis of novel arginine vasopressin prodrugs.

Mercury-Free Automated Synthesis of Guanidinium Backbone Oligonucleotides

A new method for synthesizing deoxynucleic guanidine (DNG) oligonucleotides that uses iodine as a mild and inexpensive coupling reagent is reported. This method eliminates the need for the toxic mercury salts and pungent thiophenol historically used in methods aimed at preparing DNG oligonucleotides. This coupling strategy was readily translated to a standard MerMade 12 oligonucleotide synthesizer with coupling yields of 95% and has enabled the synthesis of a 20-mer DNG oligonucleotide, the longest DNG strand to date, in addition to mixed DNA-DNG sequences with 3-9 DNG inserts. Importantly, DNG oligonucleotides exhibit robust unaided cellular uptake as compared to unmodified oligonucleotides without apparent cellular toxicity. Taken together, these findings should greatly increase the accessibility of cationic backbone modifications and assist in the development of oligonucleotide-based drugs.

N-Guanidyl and C-Tetrazole Leu-Enkephalin Derivatives: Efficient Mu and Delta Opioid Receptor Agonists with Improved Pharmacological Properties

Leu-enkephalin and d-Ala₂-Leu-enkephalin were modified at their N- and C-termini with guanidyl and tetrazole groups. The resulting molecules were prepared in solution or by solid phase peptide synthesis. The affinity of the different analogues at mu (MOP) and delta opioid receptors (DOP) was then assessed by competitive binding in stably transfected DOP and MOP HEK293 cells. Inhibition of cAMP production and recruitment of β-arrestin were also investigated. Finally, lipophilicity (logD_7.4) and plasma stability of each compound were measured. Compared to the native ligands, we found that the replacement of the terminal carboxylate by a tetrazole slightly decreased both the affinity at mu and delta opioid receptors as well as the half-life. By contrast, replacing the ammonium at the N-terminus with a guanidyl significantly improved the affinity, the potency, as well as the lipophilicity and the stability of the resulting peptides. Replacing the glycine residue with a d-alanine in position 2 consistently improved the potency as well as the stability of the analogues. The best peptidomimetic of the whole series, guanidyl-Tyr-d-Ala-Gly-Phe-Leu-tetrazole, displayed sub-nanomolar affinity and an increased lipophilicity. Moreover, it proved to be stable in plasma for up to 24 h, suggesting that the modifications are protecting the compound against protease degradation.

Cobalt-catalyzed condensation of sulfonyl azides with o-diisocyanoarenes and anilines: a new approach to N-sulfonyl guanidines

A novel method for the synthesis of N-sulfonyl guanidines is reported using a cobalt-catalyzed cascade reaction of sulfonyl azides with o-diisocyanoarenes and anilines.

Postelongation Strategy for the Introduction of Guanidinium Units in the Main Chain of Helical Oligourea Foldamers

The synthesis of hybrid urea-based foldamers containing isosteric guanidinium linkages at selected positions in the sequence is described. We used a postelongation approach whereby the guanidinium moiety is introduced by direct transformation of a parent oligo(urea/thiourea) foldamer precursor. The method involves activation of the thiourea by treatment with methyl iodide and subsequent reaction with amines. To avoid undesired cyclization with the preceding urea moiety, resulting in heterocyclic guanidinium formation in the main chain, the urea unit preceding the thiourea unit in the sequence was replaced by an isoatomic and isostructural γ-amino acid. The approach was extended to solid-phase techniques to accelerate the synthesis of longer and more functionalized sequences. Under optimized conditions, an octamer hybrid oligomer incorporating a central guanidinium linkage was obtained in good overall yield and purity. This work also reports data related to the structural consequences of urea by guanidinium replacements in solution and reveals that helical folding is substantially reduced in oligomers containing a guanidinium group.

A mild method for the synthesis of carbamate-protected guanidines using the Burgess reagent

A simple method for the synthesis of carbamate-protected guanidines from primary amines is described. A variety of thioureas derived from primary amines and isothiocyanates react with the Burgess reagent to give the corresponding guanidines via either a stepwise or one-pot procedure. By tuning the carbamoyl units of isothiocyanates and the Burgess reagent, differentially N,N'-diprotected guanidines can be obtained. Selective deprotection of the products affords N-monoprotected guanidines.

Guanidines: from classical approaches to efficient catalytic syntheses

This review focuses on the metal-mediated catalytic addition of amines to carbodiimides as an atom-economical alternative to the classical synthesis of guanidines.

Solid-phase synthesis of fusaricidin/LI-F class of cyclic lipopeptides: Guanidinylation of resin-bound peptidyl amines

Fusaricidins/LI-Fs and related cyclic lipopeptides represent an interesting new class of antibacterial peptides with the potential to meet the challenge of antibiotic resistance in bacteria. Our previous study (Bionda et al. ChemMedChem 2012, 7, 871-882) revealed the significance of the guanidinium group located at the termini of the lipidic tails of these cyclic lipopeptides for their antibacterial activities. Therefore, devising a synthetic strategy that will allow incorporation of guanidinium functionality into their structure is of particular practical importance. Since appropriately protected guanidino fatty acid building blocks are not commercially available, our strategy toward guanidinylated fusaricidin/LI-F analogs include solid-phase synthesis of a cyclic lipopeptide precursor possessing a lipidic tail with a terminal amino group followed by its conversion into corresponding guanidine. To find the optimal method for this conversion, we have examined commonly used guanidinylation reagents under the conditions compatible with standard solid-phase peptide synthesis. Described experimental results demonstrated superiority of N,N'-di-Boc-N″-triflylguanidine in solid-phase preparation of fusaricidin/LI-F class of cyclic lipopeptides. The triflylguanidine reagent gave a single monoguanidinylated product in excellent yield independently of the type of solid-support.

Synthesis of a Thermostable Polymer-supported Strongly Basic Catalyst and its Catalytic Activity

A novel strongly basic polymer-supported catalyst with guanidine groups has been synthesized and its thermal stability has been investigated. To obtain a thermally stable, cross-linked structure, guanidine groups bound to a polystyrene matrix were allowed to react in a nucleophilic manner with p-xylylene dichloride. Compared with the conventional strongly basic anion-exchange resin 201, it possesses higher thermal stability when placed in deionized water at 95°C for 60 h. This was confirmed by thermogravimetric analysis. The excellent thermal stability can be attributed to the unique structure of guanidine and the cross-linking connection mode between this base and the polymeric matrix. The obtained resin was found to efficiently catalyze Knoevenagel condensation reactions with remarkably high yields. Furthermore, the catalytic efficiency of the resin was found to remain unaffected for seven cycles, whereas that of 201 resin was reduced by 25 % owing to degradation of the strongly basic groups.

Solid-phase guanidinylation of peptidyl amines compatible with standard Fmoc-chemistry: formation of monosubstituted guanidines

With the growing importance of peptides and peptidomimetics as potential therapeutic agents, a continuous synthetic interest has been shown for their modification to provide more stable and bioactive analogs. Among many approaches, peptide/peptidomimetic guanidinylation offers access to analogs possessing functionality with strong basic properties, capable of forming stable intermolecular H-bonds, charge pairing, and cation-π interactions. Therefore, guanidinium functional group is considered as an important pharmacophoric element. Although a number of methods for solid-phase guanidinylation reactions exist, only a few are fully compatible with standard Fmoc solid-phase peptide chemistry.In this chapter we summarize the solid-phase guanidinylation methods fully compatible with standard Fmoc-synthetic methodology. This includes use of direct guanidinylating reagents such as 1-H-pyrazole-1-carboxamidine and triflylguanidine, and guanidinylation with di-protected thiourea derivatives in combination with promoters such as Mukaiyama's reagent, N-iodosuccinimide, and N,N'-diisopropylcarbodiimide.

Guanidylated hollow fiber membranes based on brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) for gold sorption from acid solutions

Novel guanidylated hollow fiber membranes are prepared based on brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) under mild reaction conditions. 1H-pyrazole-1-carboxamidine hydrochloride (HPCA) is employed for the guanidylation in aqueous solution at room temperature. The obtained guanidylated PPO hollow fiber membranes (GPPO HFMs) contain 0.31-0.95 mmol/g guanidyl groups and show high affinity to tetrachloroauric anions (AuCl(4)(-)) in acid solutions. For 0.1M HCl solution containing 57.8 mg gold/L, the sorption amount can get as high as 130 mg/g. Besides, the GPPO HFMs show preferable selectivity toward gold in multicomponent solution containing Mg(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II). A system of comparison experiments involving the sorption behavior of GPPO HFMs and quaternary aminated HFMs are also performed. The results reveal that driving forces for the high adsorption of gold mainly involve complexation mechanism. Overall, the obtained GPPO HFM is a promising chelating material for the recovery of gold.

MMT, Npeoc-protected spermine, a valuable synthon for the solid phase synthesis of oligonucleotide oligospermine conjugates via guanidine linkers

Solid phase spermine oligomerization via guanidine linkers was achieved using activated thiourea coupling reaction with primary amino group. Disymmetric spermine synthon was efficiently synthesised in eight steps from spermine. MMT group was used as coupling monitor and resulting oligomeric spermines were conjugated to oligonucleotides.

Parallel Solution-Phase Synthesis of 2-Alkylthio-5-arylidene-3,5-dihydro-4H-imidazol-4-one by One-Pot Three-Component Domino Reaction

A practical protocol for the preparation of a parallel solution-phase library of 5-arylidene imidazolone is reported. Target compounds were obtained in good yield, stereoselectively, and purity by one-pot domino reaction from various thiohydantoines, arylaldimines, and halogenoalkanes. Purification of the final products by recrystallization with a mixture of pentane/ethanol allowed simple isolation of the 17 components of the array.

Organic azides: an exploding diversity of a unique class of compounds

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aubé rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Structure–activity relationship studies on niphimycin, a guanidylpolyol macrolide antibiotic. Part 1: The role of the N-methyl-N″-alkylguanidinium moiety

Several N-methyl-N''-alkylguanidinium derivatives were synthesized and used as simplified analogues of niphimycin (NM), a guanidylpolyol macrolide, in structure-activity relationship studies. The C16-alkylated derivative exerted fungicidal activity by directly damaging the fungal plasma membrane and inducing oxidative stress in a manner similar to niphimycin. These results indicate that the N-methyl-N''-alkylguanidinium moiety is required for antifungal activity by NM.

Solid-Phase and Solution-Phase Syntheses of Oligomeric Guanidines Bearing Peptide Side Chains

[reaction: see text] Synthetic strategies for preparing N,N'-bridged oligomeric guanidines bearing peptide side chains both on solid support and in solution are presented. Monomers are prepared from common alpha-amino acids and therefore contain conventionally protected peptide side chains. The side chains include alkyl, aromatic, hydroxyl, amino, carboxylic acid, and amide functional groups. Oligomer elongation utilizes acid-sensitive sulfonyl activated thiourea through the formation of carbodiimide intermediate. With proper preparation of monomers, synthesis of oligomer can be performed in two directions (equivalent to N to C terminal or C to N terminal in a peptide sequence) with excellent efficiency.

A New Linker for Anchoring/Masking Primary Amines on Solid Support

A polymer-supported diketone was synthesized and used to fully protect/mask primary amines by the formation of a pyrrole ring. Various reactions can be performed on this system which then can be cleaved with full restoration of the amine functionality. The resin can also be recycled at least once without loss of purity of the final compound. [structure: see text]

A 1,3-Diaza-Claisen Rearrangement that Affords Guanidines

[reaction: see text] N-Alkyl-N'-tosylthioureas activated by EDCI react with azanorbonenes at room temperature through a 1,3-diaza-Claisen rearrangement, affording highly substituted, bicyclic guanidines in moderate to good yields.

Design, synthesis and biological activity of a targeted library of potential tryptase inhibitors

We have designed, synthesized, and tested two small collections of potential tryptase inhibitors. The first library consists of diversely N-substituted 3-aminopiperidin-2-ones 6, and the second (compounds 7) was prepared by dimerising compounds 6 through the 3-amino function using diverse carbon chains. We have established efficient routes for obtaining 6 both in solution and on solid supports. We have also compared the dimerisation on-resin and in solution. Four of the compounds showed a high degree of tryptase inhibition at 1 microM, but none surpassed the tryptase inhibition activity of BABIM.

A “Catch and Release” Strategy for the Parallel Synthesis of 2,4,5-Trisubstituted Pyrimidines

A resin capture and release strategy for making a combinatorial array of 2,4,5-trisubstituted pyrimidines is demonstrated by capturing beta-ketoesters and beta-ketoamides on a solid-supported piperazine. Through a cyclocondensation reaction, the solid-supported enaminone is reacted with several guanidines under heating or microwave irradiation affording the corresponding pyrimidines in good yield and chemical purity directly on solution. After this final step, the support can be effectively recycled.

Solid phase synthesis and application of trisubstituted thioureas

Resin-bound amines 1a-e condense with isothiocyanates to give thiourea resins 2a-i. Resins 2a-g subsequently react with iodomethane followed by cleavage affording S-methyl isothioureas 4a-g, and resins 2a-b,h-i react with acyl chlorides to afford N-acylated thioureas 6a-d. N-Acylthioureas 8a-f (R(2) = H) were prepared directly from resin-bound amines 1a-d with acyl isothiocyanates. N-Acylthioureas 8a-d,f(R(2) = H) were used for the preparation of S-methyl-N-acylisothioureas 10a-e. Alkylation was performed using methyl iodide. Resin-bound S-methyl-N-acylisothioureas 10a,b,d are converted by an action of hydrazines into 3-amino-1,2,4-triazoles 13a-d. Condensation of resins 8a-e (R(2) = H) with 2-bromoacetophenones in the presence of TEA affords thiazoles 15 a-e. All transformations proceeded in high yields and gave products of good purities.

Potentiation of BCNU cytotoxicity by molecules targeting abasic lesions in DNA

We describe the synthesis, DNA binding measurements and pharmacological properties of a series of new heterodimeric molecules, in which a 2,6-diaminopurine is linked to a 9-aminoacridine chromophore. The linking chain contains a central N,N'-disubstituted guanidine, connected to the two chromophores by polymethylenic units of variable length.

Substituted guanidines: introducing diversity in combinatorial chemistry

The guanidine moiety is an important motif present in many biologically active compounds. Fully substituted guanidines are of key importance for the development of bioactive molecules. The present paper reports on an efficient procedure for the direct solid-phase conversion of amines to fully substituted guanidines under very mild conditions.

Solid-phase synthesis of substituted guanidines using a novel acid labile linker

A novel acid labile linker for solid-phase synthesis of substituted guanidines has been developed. Its synthetic utility is exemplified by high-yielding pyrazole displacement with structurally and electronically diverse sets of aliphatic and aromatic amines. The final cleavage is achieved by treatment with 95:5 trifluoroacetic acid/water for 1 h. The corresponding guanidines were obtained in high purity (80-95%) and good isolated yields (50-95%). The scope and limitations of this linker were further demonstrated by the solid-phase synthesis of an 880-member library of individual trisubstituted arylguanidines employing pyrazole displacement with a set of 11 anilines and two subsequent Mitsunobu N-alkylations with sets of 10 and 8 alcohols, respectively.

Solution- and solid-phase syntheses of substituted guanidinocarboxylic acids

A library of guanidine-based compounds was produced to mimic the lead compound 1, which is a substance known to have intensely sweet-taste characteristics. Libraries of guanidinocarboxylic acids were therefore prepared via two synthetic methods. The solid-phase method involving trapping of solution-phase carbodiimides by supported amines was used to produce N,N'-dialkyl derivatives (Scheme 1). The second solid-phase method, featuring supported carbodiimides and solution-phase amines (Scheme 2), was devised to prepare N,N'-disubstituted and N,N',N'-trisubstituted guanidinocarboxylic acids. A small collection of guanadinoacetic acid dimers and trimers was also prepared, but this time via a solution-phase coupling of carbodiimides to a polyamine linker.