Combinatorial chemistry of hydantoins

C-Terminal-Modified Oligourea Foldamers as a Result of Terminal Methyl Ester Reactions under Alkaline Conditions

Hybrids of short oligourea foldamers with residues of α, β and γ-amino acids esters at the C-terminus were obtained and subjected to a reaction with LiOH. There are two possible transformations under such conditions, one of which is ester hydrolysis and the formation of a carboxylic group and the other is the cyclization reaction after abstraction of a proton from urea by a base. We have investigated this reaction with difference C-terminal residue structures, as well as under different work-up conditions, especially for oligourea hybrids with α-amino acid esters. For these compounds, an oligourea-hydantoin combination is the product of cyclization. The stability of the hydantoin ring under alkaline conditions has been alsotested. Furthermore, this work reports data related to the structure of C-terminal-modified oligourea foldamers in solution and, for one compound, in the solid state. Helical folding is preserved both for cyclized and linear modifications, with oligourea-acid hybrids appearing to be more conformationally stable, as they are stabilized by an additional intramolecular hydrogen bond in comparison to cyclic derivatives.

An Old Story in the Parallel Synthesis World: An Approach to Hydantoin Libraries

An approach to the parallel synthesis of hydantoin libraries by reaction of in situ generated 2,2,2-trifluoroethylcarbamates and α-amino esters was developed. To demonstrate utility of the method, a library of 1158 hydantoins designed according to the lead-likeness criteria (MW 200-350, cLogP 1-3) was prepared. The success rate of the method was analyzed as a function of physicochemical parameters of the products, and it was found that the method can be considered as a tool for lead-oriented synthesis. A hydantoin-bearing submicromolar primary hit acting as an Aurora kinase A inhibitor was discovered with a combination of rational design, parallel synthesis using the procedures developed, in silico and in vitro screenings.

Self-assembling α,γ-cyclic peptides that generate cavities with tunable properties

The design and synthesis of β-sheet-based self-assembling cyclic peptides with tunable cavities is described. The incorporation of a γ-amino acid with a hydroxyl group at C2 allows the incorporation of different groups that modify the internal properties of the resulting dimeric ensemble. These dimers can entrap different guests depending on the properties of the group at C2. The guest defines the geometry of the resulting aggregate.

Molecular structure, tautomeric stability, protonation and deprotonation effects, vibrational, NMR and NBO analyses of 2,4-Dioxoimidazolidine-5-acetic acid (DOIAA) by quantum chemical calculations

This study represents the conformation, tautomeric stability, protonation and deprotonation effects, vibrational, electronic, NBO and NMR aspects of 2,4-Dioxoimidazolidine-5-acetic acid (DOIAA). Theoretical calculations were performed by ab initio HF and density functional theory (DFT)/B3LYP method using 6-311++G(d,p) basis sets. Tautomerism and the effect of solvent on the tautomeric equilibria in the gas phase and in different solvents were studied. The protonation and deprotonation effects on the reactivity and conformations of DOIAA were investigated. Electronic transitions were also studied and the most prominent transition corresponds to π→π*. Natural bond orbital (NBO) analysis was also carried out to find the intramolecular interactions and their stabilization energy. In DOIAA, the interaction between the lone pair donor orbital (n(LP1N5)) and the acceptor antibonding orbital π*(C6O7) reveals the strong stabilization energy of 224.9 kJ mol(-1). Molecular electrostatic potential (MEP) was calculated to predict the reactive sites of the title compound. The NMR results indicated that the observed chemical shifts for NH, COOH protons of DOIAA not only depend on the structure of the molecule being studied but also on the nature of the solvent, concentration of the sample and the presence of the other exchangeable protons.

Parallel Solid-Phase Synthesis of disubstituted 3-(1H-benzo[d]imidazol-2-yl)imidazolidine-2,4-diones and 3-(1H-benzo[d]imidazol-2-yl)-2-thioxoimidazolidin-4-ones

A multistep approach to construct novel 3-(1H-benzo[d]imidazol-2-yl)imidazolidine-2,4-diones and 3-(1H-benzo[d]imidazol-2-yl)-2-thioxoimidazolidin-4-ones from commercially available amino acids, amines, and carboxylic acids is described. Coupling of Fmoc-amino acid to resin-bound aminobenzimidazole provided following Fmoc elimination free amine. Treatment of the free amine with 1,1'-carbonyldiimidazole or 1,1'-thiocarbonyldiimidazole furnished the corresponding hydantoins and thiohydantoins via intramolecular cyclization. The desired aminobenzimidazole tethered hydantoin or thiohydantoins were isolated in good yields.

Solid-phase synthesis of a library of amphipatic hydantoins. Discovery of new hits for TRPV1 blockade

Some heterocyclic systems, called privileged scaffolds, appear frequently in bioactive products and marketed drugs. The combination of a recognized privileged scaffold (hydantoin) and a functional group with high incidence in bioactive molecules (guanidine) guided the design of a library of amphipatic compounds, which allowed the discovery of novel TRPV1 ion channel blockers. The library was synthesized by parallel solid-phase synthesis from an orthogonally protected resin-bound Lys-Lys skeleton. Key steps of the synthetic procedure were the construction of the hydantoin ring, by reaction of the N-terminal amino group with N,N-disuccinimidyl carbonate (DSC) and subsequent base-induced cyclization, and the guanidinylation of the C-terminal Lys side-chain after removal of the Alloc protecting-group. The preliminary biological studies have allowed the identification of some of the key structural features directing the blockage of capsaicin-induced Ca(2+) influx through TRPV1 channels, particularly, the strong preference showed for highly lipophilic acyl groups and substituted guanidine moieties. Active compounds based on this new pharmacophoric scaffold that display in vitro and in vivo inhibitory activity.

Solid-phase synthesis of disubstituted N-acylureas from resin-bound ureas and acyl chlorides

Acylureas (ureides) are valued for their important biological activities. Whereas cyclic acylureas have frequently been the object of solid-phase chemistry, only few reports have focused on the solid-supported preparation of acyclic representatives. We have prepared different types of acylureas on Rink amide resin in three or four steps. The products are either N-acylated (9, 18), N-acylated-N'-alkylated (10, 19), or N-acylated-N-alkylated (22). Characteristic NMR parameters of isomeric acylureas 10, 19, and 22 are discussed.

Introduction of functional groups into peptides via N-alkylation

An optimized protocol for the mild and selective Fukuyama-Mitsunobu reaction was used for mono- and di- N-alkylation on solid support. Thereby, nonfunctionalized aliphatic and aromatic residues are quickly introduced into transiently protected, primary amines of a linear peptide. N-Alkylation can also be used to implement alkyl chains carrying (protected) functionalities suited for subsequent modification. Applicability of this method is demonstrated by various N-alkylated analogues of a cyclic CXCR4 receptor antagonist originally developed by Fujii et. al.

Synthesis of 1,3,5-trisubstituted hydantoins by regiospecific domino condensation/aza-Michael/O-->N acyl migration of carbodiimides with activated alpha,beta-unsaturated carboxylic acids

[reaction: see text] Carbodiimides and suitably activated alpha,beta-unsaturated carboxylic acids react effectively to afford a vast array of 1,3,5-trisubstituted hydantoins by means of a regiospecific domino condensation/aza-Michael/N-->O acyl migration. The reaction works well in very mild conditions (20 degrees C, dichloromethane) with fumaric acid derivatives bearing an electron-withdrawing group in the beta position. Good results have been obtained also with less activated substrates bearing only one electron-withdrawing group in the beta position, using more polar solvents (acetonitrile, DMF), and in the presence of a base (2,4,6-trimethylpyridine). Reactions with asymmetric carbodiimides are generally highly chemo- and regioselective, giving rise to the formation of a single regioisomeric hydantoin. However, asymmetric carbodiimides bearing one alkyl group and one aryl group can produce variable amounts of N-acylurea byproducts. The latter could be easily recovered and transformed into the corresponding hydantoins. A detailed study of the influence of key reaction parameters such as solvent, base, and structure of the reactants on the reaction outcome and mechanism is presented. This methodology is particularly convenient for the synthesis of trifluoromethyl-substituted hydantoins, which could be interesting as bioactive compounds in medicinal chemistry, as well as precursors of the corresponding alpha-amino acids.

The aminobarbituric acid-hydantoin rearrangement

A general synthesis protocol for the generation of tri- and tetrasubstituted 5-carbamoylhydantoins is described. Starting from barbituric acids and following bromination and reaction with primary amines, 5-aminobarbituric acids 3a-s and 8 were prepared. Compounds 3 and 8 were subjected to different conditions of a base-catalyzed rearrangement reaction to yield the 1,5,5-trisubstituted hydantoins 4a-s and the 1,3,5,5-tetrasubstituted hydantoin 5c, respectively. Alkylation of 4a-s afforded 1,3,5,5-tetrasubstituted hydantoins 5a-h. Mechanisms that explain the transformation of corresponding aminobarbituric acids to hydantoins 4a-s and 5c were discussed in terms of the formation of ring-opened intermediates. Aminobarbituric acids 3a-s unsubstituted at position 3 underwent a ring contraction via intermediate isocyanates which were trapped by the amino function. A different mechanism involving a carbamate intermediate was concluded for conversion of the 1,3,5,5-tetrasubstituted aminobarbituric acid 8.

Comparative HPLC enantioseparation of new chiral hydantoin derivatives on three different polysaccharide type chiral stationary phases

The enantioseparation of eighteen new chiral hydantoin derivatives was studied on three different polysaccharide type chiral stationary phases (CSP) Chiralpak AD, Chiralcel OD and Chiralcel OJ in the normal-phase HPLC mode. Chiralpak AD material exhibited the most universal chiral resolving ability and allowed the enantioseparation of 17 out of 18 compounds followed by Chiralcel OD (10 enantioseparations of 12 tested compounds) and Chiralcel OJ (eight enantioseparation from 13 tested analytes). Some complementary separations were observed and all of 18 compounds could be resolved at least with one of the three chiral CSP under the conditions of this study. With regard to the structure of the analytes, bulky electron rich substituents at C5 of the hydantoin nucleus appear to favor stereoselective interactions.

Solid-phase preparation of hydantoins through a new cyclization/cleavage step

An efficient process for the solid-phase synthesis of hydantoins has been developed. The amino acid starting material is anchored to the resin from its carboxylic acid end through formation of a very stable amide bond. After introduction of different functional groups, the cleavage/cyclization step can be performed in acidic or basic conditions.

Discovery of human CCR5 antagonists containing hydantoins for the treatment of HIV-1 infection

A series of hydantoin derivatives has been discovered as highly potent nonpeptide antagonists for the human CCR5 receptor. The synthesis, SAR, and biological profiles of this class of antagonists are described.

Solid-phase synthesis of peptidomimetic inhibitors for the hepatitis C virus NS3 protease

The NS3 serine protease enzyme of the hepatitis C virus (HCV) is essential for viral replication. Short peptides mimicking the N-terminal substrate cleavage products of the NS3 protease are known to act as weak inhibitors of the enzyme and have been used as templates for the design of peptidomimetic inhibitors. Automated solid-phase synthesis of a small library of compounds based on such a peptidomimetic scaffold has led to the identification of potent and highly selective inhibitors of the NS3 protease enzyme.

Tracelessness Unmasked: A General Linker Nomenclature

Nowadays it is rare to find an issue of a major chemistry journal without at least one article on solid-phase synthesis. This is hardly surprising: the technique promises an end to arduous work-up procedures and the ability to facilitate the creation of vast libraries of compounds using combinatorial techniques. No longer is the technique only of interest to those involved in peptide synthesis: an enormous variety of product classes have now been prepared on and isolated from the solid phase. It is the "linker" which is the focus of this article. The linker's ultimate function is to release a product from the support into solution: it does this, without exception, with a chemical change to the product at the former linkage site. Some linkers, apparently, are "traceless". But what, in fact, is "tracelessness"? Twenty years ago, in a climate where cleavage of a linker resulted in formation of a polar carboxylic acid as the vestige of the support, the concept was attractive. Today the chemist is faced with a myriad of novel linkers which have the ability to release products bearing most major functionalities at the former linkage site and we will argue here that the term "traceless", although currently in widespread use, is meaningless. Instead, we propose a new categorization of linkers based on the functionality they release upon cleavage, and suggest a nomenclature to underpin this categorization. We anticipate that the article will also serve to highlight areas of linker technology in need of further research.

Diastereoselective synthesis of hydantoin- and isoxazoline-substituted dispirocyclobutanoids

Synthetic strategies for constructing novel achiral cyclobutanoid isoxazolidinoimidazolidinedione heterocycles, with a generalized structure of II, have been developed via 1,3-dipolar cycloaddition and carbanilide cyclization transformations from methylenecyclobutane 13. The exo methylene cyclobutane system has made the realization of some diasteroselectivity possible, such that the H-bond (Boc-NH) directed product (i.e., 14) was obtained with 3:1 selectivity relative to the non-H-bond directed product (i.e., 15).

The solid phase synthesis of a series of tri-substituted hydantoin ligands for the somatostatin SST5 receptor

A series of trisubstituted hydantoins has been prepared by a versatile solid phase route employing primary alcohols, amines and amino acids as the monomeric building blocks. Several compounds showed submicromolar affinity in binding assays at recombinant human somatostatin receptors.