Dinuclear Zn(2+) complexes of synthetic heptapeptides as artificial nucleases

Efficient Plasmid DNA Cleavage by a Mononuclear Copper(II) Complex

The Cu(II) complex of the ligand all-cis-2,4,6-triamino-1,3,5-trihydroxycyclohexane (TACI) is a very efficient catalyst of the cleavage of plasmid DNA in the absence of any added cofactor. The maximum rate of degradation of the supercoiled plasmid DNA form, obtained at pH 8.1 and 37 degrees C, in the presence of 48 microM TACI.Cu(II), is 2.3 x 10(-3) s(-1), corresponding to a half-life time of only 5 min for the cleavage of form I (supercoiled) to form II (relaxed circular). The dependence of the rate of plasmid DNA cleavage from the TACI.Cu(II) complex concentration follows an unusual and very narrow bell-like profile, which suggests an high DNA affinity of the complexes but also a great tendency to form unreactive dimers. The reactivity of the TACI.Cu(II) complexes is not affected by the presence of several scavengers for reactive oxygen species or when measured under anaerobic conditions. Moreover, no degradation of the radical reporter Rhodamine B is observed in the presence of such complexes. These results are consistent with the operation of a prevailing hydrolytic pathway under the normal conditions used, although the failure to obtain enzymatic religation of the linearized DNA does not allow one to rule out the occurrence of a nonhydrolytic oxygen-independent cleavage. A concurrent oxidative mechanism becomes competitive upon addition of reductants or in the presence of high levels of molecular oxygen: under such conditions, in fact, a remarkable increase in the rate of DNA cleavage is observed.

Ester cleavage properties of synthetic hydroxybenzotriazoles in cationic monovalent and gemini surfactant micelles

Four new hydroxybenzotriazole derivatives have been synthesized. Two of them, N-tetradecyl-1-hydroxy-1H-benzo[d][1,2,3]triazole-6-carboxamide (2) and N-tetradecyl-1-hydroxy-1H-benzo[d][1,2,3]triazole-7-carboxamide (3), possess long alkyl chains, while the other two, 1-hydroxy-1H-benzo[d][1,2,3]triazole-6-carboxylic acid (4) and 1-hydroxy-1H-benzo[d][1,2,3]triazole-7-carboxylic acid (5), have carboxylate side chains. These compounds along with their parent unsubstituted 1-hydroxybenzotriazole (HOBt), 1, have been examined for the cleavage of p-nitrophenyl hexanoate (PNPH) and p-nitrophenyl diphenyl phosphate (PNPDPP) in comicelles with monovalent cetyltrimethylammonium bromide (CTABr) and the corresponding bis-cationic gemini surfactants 16-m-16, 2Br(-) of identical chain length at 25 degrees C and pH 8.2. The apparent pK(a) values of the HOBt derivatives in the comicelles of CTABr or 16-4-16 gemini surfactant have been determined from the rate versus pH profiles and were found to be comparable. Catalytic system 4/16-4-16 demonstrated over 2200- and 1650-fold rate enhancements in the hydrolysis of PNPDPP and PNPH, respectively, for identical reactions carried out at pH 8.2 and 25 degrees C in buffered aqueous media. The second-order rate constants for such bimolecular reactions were determined employing pseudophase micellar models. Experiments in which excess substrate was taken over HOBt derivatives demonstrated that the catalysts "turned over"; hydrolysis of the putative acylated or phosphorylated HOBt intermediates was rapid in either type of host micelles.

Helix-helix interconversion rates of short13C-labeled helical peptides as measured by dynamic NMR spectroscopy

The rates at which a peptide hexamer and a peptide octamer interconvert between left- and right-handed helical forms in CD2Cl2 solution have been characterized by 13C dynamic NMR (DNMR) spectroscopy. The peptide esters studied are Fmoc-(Aib)n-OtBu (n = 6 and 8), where Fmoc is 9-fluorenylmethyoxycarbonyl and Aib is the strongly helix-forming residue alpha-aminoisobutyric acid. Because the Aib residue is itself achiral, homooligomers of this residue form a 50/50 mixture of enantiomeric 3(10)-helices in solution. It has been demonstrated (R.-P. Hummel, C. Toniolo, and G. Jung, Angewandte Chemie International Edition, 1987, Vol. 26, pp. 1150-1152) that oligomers of Aib interconvert on the millisecond timescale. We have performed lineshape analysis of 13C-NMR spectra collected for our peptides enriched with 13C at a single residue. Rate constants for the octamer range from 6 s(-1) at 196 K to about 56,500 s(-1) at 320 K. At all temperatures, the hexamer interconverts about three times faster than the octamer. Eyring plots of the data reveal experimentally indistinguishable DeltaH++ values for the hexamer and octamer of 37.8 +/- 0.6 and 37.6 +/- 0.4 kJ mol(-1) respectively. The difference in the rates of interconversion is dictated by entropic factors. The hexamer and octamer exhibit negative DeltaS++ values of -29.0(-1) +/- 2.5 and -37.3 +/- 1.7 J K(-1) mol(-1), respectively. A mechanism for the helix-helix interconversion is proposed. and calculated DeltaG++ values are compared to the estimate for a decamer undergoing a helix-helix interconversion.

Artificial metallonucleases

The development of synthetic agents able to hydrolytically cleave DNA with high efficiency and selectivity is a fascinating challenge that will show the way to obtaining artificial nucleases able to compete with the natural enzymes. This Feature Article highlights the progress reported toward the realization of synthetic nucleases with particular attention to the strategies that can be pursued to improve efficiency and sequence selectivity.

Toward efficient Zn(II)-based artificial nucleases

A series of cis-cis-triaminocyclohexane Zn(II) complex-anthraquinone intercalator conjugates, designed in such a way to allow their easy synthesis and modification, have been investigated as hydrolytic cleaving agents for plasmid DNA. The ligand structure comprises a triaminocyclohexane platform linked by means of alkyl spacers of different length (from C(4) to C(8)) to the anthraquinone group which may intercalate the DNA. At a concentration of 5 microM, the complex of the derivative with a C(8) alkyl spacer induces the hydrolytic stand scission of supercoiled DNA with a rate of 4.6 x 10(-6) s(-1) at pH 7 and 37 degrees C. The conjugation of the metal complex with the anthraquinone group leads to a 15-fold increase of the cleavage efficiency when compared with the anthraquinone lacking Zn-triaminocyclohexane complex. The straightforward synthetic procedure employed, allowing a systematic change of the spacer length, made possible to gain more insight on the role of the intercalating group in determining the reactivity of the systems. Comparison of the reactivity of the different complexes shows a remarkable increase of the DNA cleaving efficiency with the length of the spacer. In the case of too-short spacers, the advantages due to the increased DNA affinity are canceled due to the incorrect positioning of the reactive group, thus leading to cleavage inhibition.

Correlation of Structure and Function in Oligonuclear Zinc(II) Model Phosphatases

A series of pyrazolate-based dizinc(II) complexes has been synthesized and investigated as functional models for phosphoesterases, focusing on correlations between hydrolytic activity and molecular parameters of the bimetallic core. The Zn...Zn distance, the (bridging or nonbridging) position of the Zn-bound hydroxide nucleophile, and individual metal ion coordination numbers are controlled by the topology of the compartmental ligand scaffold. Species distributions of the various dizinc complexes in solution have been determined potentiometrically, and structures in the solid state have been elucidated by X-ray crystallography. The hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) promoted by the dinuclear phosphoesterase model complexes has been investigated in DMSO/buffered water (1:1) at 50 degrees C as a function of complex concentration, substrate concentration, and pH. Coordination of the phosphodiester has been followed by ESI mass spectrometry, and bidentate binding could be verified crystallographically in two cases. Drastic differences in hydrolytic activity are observed and can be attributed to molecular properties. A significant decrease of the pK(a) of zinc-bound water is observed if the resulting hydroxide is involved in a strongly hydrogen-bonded intramolecular O(2)H(3) bridge, which can be even more pronounced than for a bridging hydroxide. Irrespective of the pK(a) of the Zn-bound water, a hydroxide in a bridging position evidently is a relatively poor nucleophile, while a nonbridging hydroxide position is more favorable for hydrolytic activity. Additionally, the metal array has to provide a sufficient number of coordination sites for activating both the substrate and the nucleophile, where phosphate diesters such as BNPP preferentially bind in a bidentate fashion, requiring a third site for water binding. Product inhibition of the active site by the liberated (p-nitrophenyl)phosphate is observed, and the product-inhibited complex could be characterized crystallographically. In that complex, the phosphate monoester is found to cap a rectangular array of four zinc ions composed of two bimetallic entities.

Selective Catalysis with Peptide Dendrimers

Peptide dendrimers incorporating 3,5-diaminobenzoic acid 1 as a branching unit (B) were prepared by solid-phase synthesis of ((Ac-A(3))(2)B-A(2))(2)B-Cys-A(1)-NH(2) followed by disulfide bridge formation. Twenty-one homo- and heterodimeric dendrimers were obtained by permutations of aspartate, histidine, and serine at positions A(1), A(2), and A(3). Two dendrimers catalyzed the hydrolysis of 7-hydroxy-N-methyl-quinolinium esters (2-5), and two other dendrimers catalyzed the hydrolysis of 8-hydroxy-pyrene-1,3,6-trisulfonate esters (10-12). Enzyme-like kinetics was observed in aqueous buffer pH 6.0 with multiple turnover, substrate binding (K(M) = 0.1-0.5 mM), rate acceleration (k(cat)/k(uncat) > 10(3)), and chiral discrimination (E = 2.8 for 2-phenylpropionate ester 5). The role of individual amino acids in catalysis was investigated by amino acid exchanges, highlighting the key role of histidine as a catalytic residue, and the importance of electrostatic and hydrophobic interactions in modulating substrate binding. These experiments demonstrate for the first time selective catalysis in peptide dendrimers.

Nickle(II) and cobalt(II) complexes of hydroxyl-substituted triazamacrocyclic ligand as potential antitumor agents

The stability constants for the formation of nickel(II) and cobalt(II) complexes of the ligand [1,4,7]triazecan-9-ol (L) were presented. Antitumor activity of two complexes was reported. Nuclei of [NiL]-stimulated BEL-7402 cells clearly exhibited condensation and break down into chromatin clumps typical of apoptosis. Also it exhibited perturbation effects to cell cycle, and optimal induction of apoptosis was found by Flow-Cytometric analysis. But CoL complex did not exhibit introduction effects to BEL-7402 cells apoptosis; and could not perturb cell cycle. NiL and CuL complexes could cleave supercoiled DNA (pBR 322 DNA) to nicked and linear DNA, and DNA of cells treated with NiL or CuL complex was obviously damaged; while CoL complex only could cleave supercoiled DNA (pBR 322 DNA) to nicked DNA, and DNA of cells treated with CoL complex had no significant difference with control.

Evidence of Enhanced Reactivity of DAAP Nucleophiles toward Dephosphorylation and Deacylation Reactions in Cationic Gemini Micellar Media

4,4'-(Dialkylamino)pyridine (DAAP)-based compounds 1-4 catalytically cleave hydrophobic organophosphate and carboxylate esters in various host micellar aggregates at mildly alkaline pH. The role of the micellar reaction medium in such esterolytic reactions has been carefully examined in this work. The cationic gemini surfactant based micellar aggregates provide more than 1 order of magnitude better reaction medium for the above reactions than their conventional single-chain, single-charge, cationic cetyl trimethylammonium bromide (CTABr) micelles. The catalytic turnover behavior of DAAP nucleophiles in the presence of excess substrates is also retained in gemini micellar media.

Co-ordination chemistry of amino pendant arm derivatives of 1,4,7-triazacyclononane

The binding properties of 1,4,7-triazacyclononane ([9]aneN3) to metal cations can be adapted through sequential functionalisation of the secondary amines with aminoethyl or aminopropyl pendant arms to generate ligands with increasing numbers of donor atoms. The new amino functionalised pendant arm derivative of 1,4,7-triazacyclononane ([9]aneN3), L1, has been synthesised and its salt [H2L1]Cl2 characterised by X-ray diffraction. The protonation constants of the ligands L1-L4 having one, two or three aminoethyl or three aminopropyl pendant arms, respectively, on the [9]aneN3 framework, and the thermodynamic stabilities of their mononuclear complexes with CuII and ZnII have been investigated by potentiometric measurements in aqueous solutions. In order to discern the protonation sites of ligands L1-L4, 1H NMR spectroscopic studies were performed in D2O as a function of pH. While the stability constants of the CuII complexes increase on going from L1 to L2 and then decrease on going from L2 to L3 and L4, those for ZnII complexes increase from L1 to L3 and then decrease for L4. The X-ray crystal structures of the complexes [Cu(L1)(Br)]Br, [Zn(L1)(NO3)]NO3, [Cu(L2)](ClO4)2, [Ni(L2)(MeCN)](BF4)2, [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O have been determined. In both [Cu(L1)(Br)]Br and [Zn(L1)(NO3)]NO3 the metal ion is five co-ordinate and bound by four N-donors of the macrocyclic ligand and by one of the two counter-anions. The crystal structures of [Cu(L2)](ClO4)2 and [Ni(L2)(MeCN)](BF4)2 show the metal centre in slightly distorted square-based pyramidal and octahedral geometry, respectively, with a MeCN molecule completing the co-ordination sphere around NiII in the latter. In both [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O the metal ion is bound by all six N-donors of the macrocyclic ligand in a distorted octahedral geometry. Interestingly, and in agreement with the solution studies and with the marked preference of CuII to assume a square-based pyramidal geometry with these types of ligands, the reaction of L4 with one equivalent of Cu(BF4)2.4H2O in MeOH at room temperature yields a square-based pyramidal five co-ordinate CuII complex [Cu(L6)](BF4)2 where one of the three propylamino pendant arms of the starting ligand has been cleaved to give L6.

Coordination Properties of New Bis(1,4,7-triazacyclononane) Ligands: A Highly Active Dizinc Complex in Phosphate Diester Hydrolysis

The synthesis and characterization of three new bis([9]aneN(3)) ligands, containing respectively 2,2'-bipyridine (L(1)), 1,10-phenanthroline (L(2)), and quinoxaline (L(3)) moieties linking the two macrocyclic units, are reported. Proton binding and Cu(II), Zn(II), Cd(II), and Pb(II) coordination with L(1)-L(3) have been studied by potentiometric titrations and, for L(1) and L(2), by spectrophotometric UV-vis measurements in aqueous solutions. All ligands can give stable mono- and dinuclear complexes. In the case of L(1), trinuclear Cu(II) complexes are also formed. The stability constants and structural features of the formed complexes are strongly affected by the different architecture and binding properties of the spacers bridging the two [9]aneN(3) units. In the case of the L(1) and L(2) mononuclear complexes, the metal is coordinated by the three donors of one [9]aneN(3) moiety; in the [ML(2)](2+) complexes, however, the phenanthroline nitrogens are also involved in metal binding. Finally, in the [ML(3)](2+) complexes both macrocyclic units, at a short distance from each other, can be involved in metal coordination, giving rise to sandwich complexes. In the binuclear complexes each metal ion is generally coordinated by one [9]aneN(3) unit. In L(1), however, the dipyridine nitrogens can also act as a potential binding site for metals. The dinuclear complexes show a marked tendency to form mono-, di-, and, in some cases, trihydroxo species in aqueous solutions. The resulting M-OH functions may behave as nucleophiles in hydrolytic reactions. The hydrolysis rate of bis(p-nitrophenyl)phosphate (BNPP) was measured in aqueous solution at 308.1 K in the presence of the L(2) and L(3) dinuclear Zn(II) complexes. Both the L(2) complexes [Zn(2)L(2)(OH)(2)](2+) and [Zn(2)L(2)(OH)(3)](+) and the L(3) complex [Zn(2)L(3)(OH)(3)](+) promote BNPP hydrolysis. The [Zn(2)L(3)(OH)(3)](+) complex is ca. 2 orders of magnitude more active than the L(2) complexes, due both to the short distance between the metal centers in [Zn(2)L(3)(OH)(3)](+), which could allow a bridging interaction of the phosphate ester, and to the simultaneous presence of single-metal bound nucleophilic Zn-OH functions. These structural features are substantially corroborated by semiempirical PM3 calculations carried out on the mono-, di-, and trihydroxo species of the L(3) dizinc complex.

DNA strand scission by a Cu(I).adenylated polymeric template: preliminary mechanistic and recycling studies

Cleavage of a model phosphate ester and supercoiled plasmid DNA by a Cu(I).adenylated polymer template and preliminary mechanistic investigations are reported. A novel paradigm for the design of recyclable nucleolytic reagents allowing multiple use of this catalyst is also demonstrated

Synthesis of new Cu(II)-chelating ligand amphiphiles and their esterolytic properties in cationic micelles

Four new tetradentate 2,6-disubstituted pyridine and tridentate 2-substituted pyridine ligands were synthesized. Two of these compounds possessed a metal ion binding subunit in the form of a 2,6-disubstituted-4-N,N'-dimethylamine pyridine moiety. Cu(2+)-complexes of these ligands incorporated in cetyltrimethylammonium bromide (CTABr) micelles speeded the cleavage of p-nitrophenyldiphenyl phosphate and p-nitrophenyl hexanoate at pH 7.6. On the basis of a kinetic version of Job plot analysis, a 1:1 ligand/Cu(2+) stoichiometry was found to be the most active species. In CTABr micelles, the pK(a) values for the Cu(2+)-coordinated hydroxyl or pendant -CH(2)OH in these ligands were between 7.8 and 7.9. The metallomicellar systems displayed catalytic (turnover) behavior in the presence of excess substrates.

DNA cross-linking with metallointercalator-peptide conjugates

Short peptides have been tethered to a DNA-intercalating ruthenium complex to create a photoactivated cross-linking reagent. The ruthenium complex, [Ru(phen)(bpy')(dppz)]2+ (phen = 1,10-phenanthroline, bpy' = 4-(butyric acid)-4'-methyl-2,2'-bipyridine, and dppz = dipyridophenazine), delivers the peptide to DNA and initiates the cross-linking reaction by oxidizing DNA upon irradiation in the presence of an oxidative quencher. The tethered peptide, only five to six residues in length, forms cross-links with the oxidized site in DNA. Cross-linking was detected and studied by gel electrophoresis and through spectroscopic measurements. The ruthenium-peptide complex is luminescent when bound to DNA, and the binding constants for several intercalator-peptide conjugates were determined by luminescence titration. The composition of the peptide affects both binding affinity and the extent of cross-linking. The greatest amounts of cross-linking were observed with tethered peptides that contained positively charged residues, either lysine or arginine. To test the impact of individual residues on cross-linking, the central residue in a 5-mer peptide was substituted with seven different amino acids. Though mutation of this position had only a small effect on the extent of cross-linking, it was discovered that peptides containing Trp or Tyr gave a distinctive pattern of products in gels. In experiments using the untethered peptide and ruthenium complex, it was determined that delivery of the peptide by the ruthenium intercalator is not essential for cross-linking; peptide attachment to the metal complex can constrain cross-linking. Importantly, the cross-linking adducts produced with ruthenium-peptide conjugates are luminescent and thus provide a luminescent cross-linking probe for DNA.

A peptide template as an allosteric supramolecular catalyst for the cleavage of phosphate esters

The heptapeptide H-Iva-Api-Iva-ATANP-Iva-Api-Iva-NHCH(3) (P1a), where Iva is (S)-isovaline, Api is 4-amino-4-carboxypiperidine, and ATANP is (S)-2-amino-3-[1-(1,4,7-triazacyclononane)]propanoic acid, has been synthesized. Its conformation in aqueous solution is essentially that of a 3(10)-helix. By connecting three copies of P1a to a functionalized Tris(2-aminoethyl)amine (Tren) platform a new peptide template, [T(P1)(3)], was obtained. This molecule is able to bind up to four metal ions (Cu(II) or Zn(II)): one in the Tren subsite and three in the azacyclononane subunits. The binding of the metals to the Tren platform induces a change from an open to a closed conformation in which the three short, helical peptides are aligned in a parallel manner with the azacyclonane units pointing inward within the pseudocavity they define. T(P1)(3) shows a peculiar behavior in the transphosphorylation of phosphate esters; the tetrazinc complex is a catalyst of the cleavage of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP), whereas the free ligand is a catalyst of the cleavage of an oligomeric RNA sequence with selectivity for pyrimidine bases. In the case of HPNP, Zn(II) acts as a positive allosteric effector by enhancing the catalytic efficiency of the system. In the case of the polyanionic RNA substrate, Zn(II) switches off the activity, thus behaving as a negative allosteric regulator. It is suggested that the opposite behavior of the catalyst induced by Zn(II) is associated with the change of conformation of the Tren platform, and consequently of the relative spatial disposition of the three linked peptides, that occurs after binding of the metal ion.

A helical peptide receptor for [60]fullerene

Two terminally blocked nonapeptides, each made up of six Aib residues, a Gly spacer and two L-Tyr residues in positions 2 and 8 (these are substituted in the side chain with either ferrocenoyl or methyl moieties), have been synthesized by solution methods and fully characterized. FT-IR absorption and two-dimensional NMR analyses indicate that a 3(10)-helical conformation is adopted by these rigid peptides in structure-supporting solvents. An X-ray diffraction investigation shows that the bis-L-Tyr(Me) nonapeptide in the crystal state is folded in a regular right-handed 3(10)-helical structure. As five amino acid units separate the two substituted L-Tyr residues in the peptide sequence, the two side chain moieties will-in solution-face each other after two complete turns of the ternary helix. By carrying out a detailed photophysical analysis, we have demonstrated that the electron-rich, hydrophobic and wide cavity generated by the nonapeptide template with two ferrocenoyloxybenzyl walls is able to host [60]fullerene. Further evidence for this superstructure has been provided in the gas phase by a mass spectrometric investigation.

A concise, modular synthesis of chiral peraza-macrocycles using chiral aziridines

[reaction: see text] Novel chiral peraza-macrocycles were synthesized from chiral aziridines as a common building block. Efficient syntheses of chiral [26]-N(6), [12]-N(4), [9]-N(3), and [14]-N(4) systems were accomplished.

DNA hydrolysis and oxidative cleavage by metal-binding peptides tethered to rhodium intercalators

With the goal of developing artificial nucleases for DNA hydrolysis, metal-coordinating peptides have been tethered to a DNA-intercalating rhodium complex to deliver metal ions to the sugar-phosphate backbone. The intercalator, [Rh(phi)(2)bpy']Cl(3) [phi = 9,10-phenanthrenequinone diimine; bpy' = 4-(butyric acid)-4'-methyl-2,2'-bipyridine], provides DNA binding affinity, and a metal-binding peptide contributes reactivity. This strategy for DNA hydrolysis is a general one, and zinc(II)-promoted cleavage has been demonstrated for two widely different tethered metallopeptides. An intercalator coupled with a de novo-designed alpha helix containing two histidine residues has been demonstrated to cleave both supercoiled plasmid and linear DNA substrates. Mutation of this peptide confirms that the two histidine residues are essential for Zn(2+) binding and cleavage. Zinc(II)-promoted cleavage of supercoiled plasmid has also been demonstrated with an intercalator-peptide conjugate containing acidic residues and modeled after the active site of the BamHI endonuclease. Other redox-active metals, such as copper, have been delivered to DNA with our intercalator-peptide conjugates to effect oxidative chemistry. Copper cleavage experiments and photocleavage experiments with [Rh(phi)(2)bpy'](3+) complement the hydrolysis studies and provide structural information about the interactions between the tethered metallopeptides and DNA. Variation of the rhodium intercalator was also explored, but with a mismatch-specific intercalator, no site-specific hydrolysis was found. These experiments, in which the peptide, the metal cation, and the intercalator components of the conjugate are each varied, illustrate some of the issues involved in creating an artificial nuclease with DNA intercalators and metallopeptides.

Chemical nucleases

Substantial progress is being made in the synthesis of functional mimics of metallonuclease enzymes, although a comparison with enzyme-promoted rates of reaction shows considerable room for future improvement. Improved ligand design allows facile substrate binding to metal ion catalysts, while maintaining the stability of the metal complex. The execution of double-strand cleavage of DNA under hydrolytic conditions has been reported and new levels of activity achieved. Finally, considerable progress has been made in identifying the molecular determinants for site-selective cleavage of RNA (in particular) and the design of ligands to achieve targeted recognition and cleavage.

Synthesis of novel derivatives of 1,4,7-triazacyclononane

[structure: see text]. The coordination environment of 1,4,7-triazacyclononane can be adapted, through sequential functionalization of two secondary amines, to generate ligands applicable in biomimetic studies. Two "amino acids" and an amino derivative have been prepared from 1,4,7-triazatricyclo[5.2.1.0(4,10)]decane. This synthon allows efficient attachment of one functional group to the macrocyclic ring, forming a monoamidinium salt. Hydrolysis generates a formyl derivative, which was further functionalized at the secondary amine and hydrolyzed in strong acid to generate ligands 1-3.

Emerging principles of de novo catalyst design

Considerable progress has been made in the understanding of how to exploit hydrophobic and charge-charge interactions in forming binding sites for peptides and small molecules in folded polypeptide catalysts. This knowledge has enabled the introduction of feedback and control functions into catalytic cycles and the construction of folded polypeptide catalysts that follow saturation kinetics. Major advances have also been made in the design of metalloproteins and metallopeptides, especially with regards to understanding redox potential control.