Negishi Cross-Coupling Provides Alkylated Tryptophans and Tryptophan Regioisomers

Mild transition-metal catalysed cross-couplings enable direct functionalisation of biocatalytically halogenated tryptophans with alkyl iodides, representing a new alternative for late-stage derivatisations of halogenated aromatic amino acids. Moreover, this strategy enables preparation of (homo)tryptophan regioisomers in a simple two-step synthesis using a Pd-catalysed Negishi cross coupling. This method provides access to non-canonical constitutional surrogates of tryptophan, ready for use in peptide synthesis.     

Role of cationic gemini surfactants toward enhanced ninhydrin–tryptophan reaction

In this paper we report the effect of dicationic ‘gemini’ surfactants (CH₃)₂C₁₆H₃₃N⁺? (CH₂)_m? N⁺C₁₆H₃₃(CH₃)₂, 2Br^? (where m = 4, 5, 6) on the reaction of ninhydrin with DL ‐tryptophan. The gemini surfactant micellar media are comparatively more effective than their conventional monomeric counterpart cetyltrimethylammonium bromide (CTAB) micelles. Also, whereas typical rate constant (k_ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produce a third region of increasing k_ψ at higher concentrations. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in ¹H NMR line widths. Quantitative kinetic analysis of the rate constant–[surfactant] data has been performed on the basis of modified pseudophase model. Copyright © 2007 John Wiley & Sons, Ltd.     

Tracking X‐ray‐derived redox changes in crystals of a methylamine dehydrogenase/amicyanin complex using single‐crystal UV/Vis microspectrophotometry

X‐ray exposure during crystallographic data collection can result in unintended redox changes in proteins containing functionally important redox centers. In order to directly monitor X‐ray‐derived redox changes in trapped oxidative half‐reaction intermediates of Paracoccus denitrificans methylamine dehydrogenase, a commercially available single‐crystal UV/Vis microspectrophotometer was installed on‐line at the BioCARS beamline 14‐BM‐C at the Advanced Photon Source, Argonne, USA. Monitoring the redox state of the intermediates during X‐ray exposure permitted the creation of a general multi‐crystal data collection strategy to generate true structures of each redox intermediate.     

Development and reproducibility of a novel high‐performance liquid‐chromatography monolithic column method for the detection and quantification of trans‐indolyl‐3‐acryloylglycine in human urine

Elevated levels of trans‐indolyl‐3‐acryloylglycine (IAcrGly) have been reported in the urine of people with various conditions including pervasive developmental disorders (PDDs) such as autism and Asperger syndrome. Reversed‐phase high‐performance liquid chromatography with ultra‐violet detection using traditional particle silica‐based columns subsequent to solid‐phase extraction (SPE) has been the preferred assay method; requiring long analytical run times, high flow rates and high solvent usage. Recent developments in monolithic HPLC column technology facilitated the development of a novel analytical method, for the detection and quantification of urinary IAcrGly. The revised method eliminates the requirement for SPE pre‐treatment, reduces sample run‐time and decreases solvent volumes. Five urine samples from people diagnosed with PDD were run in quadruplicate to test the intra‐ and inter‐day reliability of the new method based on retention time, peak area and peak height for IAcrGly. Detection was by UV with IAcrGly confirmation by MS/MS‐MS. Relative standard deviations showed significant improvement with the new method for all parameters. The new method represents a major advancement in the detection and quantification of IAcrGly by reducing time and cost of analysis whilst improving detection limits and reproducibility. Copyright © 2009 John Wiley & Sons, Ltd.     

Modification of the Photochemical Reactions of Protein Tryptophanyls by Chloroform

The modifying action of chloroform and other halogenmethanes (difluorodichloromethane and carbon tetrachloride) on UV radiation-induced photochemical reactions of the protein tryptophanyls is shown. The effect manifests itself in an increase in the quantum yield of indole chromophore destruction and in formation of new photochemical products. It is found that the nature of the products of photochemical destruction which are formed in a tryptophan solution and in proteins is the same.     

Chemical Evolution of a Bacterial Proteome

We have changed the amino acid set of the genetic code of Escherichia coli by evolving cultures capable of growing on the synthetic noncanonical amino acid L ‐β‐(thieno[3,2‐b]pyrrolyl)alanine ([3,2]Tpa) as a sole surrogate for the canonical amino acid L ‐tryptophan (Trp). A long‐term cultivation experiment in defined synthetic media resulted in the evolution of cells capable of surviving Trp→[3,2]Tpa substitutions in their proteomes in response to the 20 899 TGG codons of the E. coli W3110 genome. These evolved bacteria with new‐to‐nature amino acid composition showed robust growth in the complete absence of Trp. Our experimental results illustrate an approach for the evolution of synthetic cells with alternative biochemical building blocks.     

Total Synthesis of cis‐Clavicipitic Acid from Asparagine via Ir‐Catalyzed CH bond Activation as a Key Step

4‐Substituted tryptophan derivatives and the total synthesis of cis‐clavicipitic acid were achieved in reactions in which Ir‐catalyzed C?H bond activation was a key step. The starting material for these reactions is asparagine, which is a cheap natural amino acid. The reductive amination step from the 4‐substituted tryptophan derivative gave cis‐clavicipitic acid with perfect diastereoselectivity.     

壳聚糖/多壁碳纳米管复合膜电化学手性识别色氨酸对映异构体

采用滴涂方式将羧酸化多壁碳纳米管(f-MWCNTs)修饰于玻碳电极(GCE)表面成膜,然后恒电位法在上述修饰电极表面电沉积壳聚糖(CS)膜,形成CS和f-MWCNTs复合膜修饰电极(CS/f-MWCNTs/GCE),并用于色氨酸(Trp)对映异构体的手性识别。采用扫描电子显微镜(SEM)表征了修饰电极表面形貌的差异,电化学阻抗(EIS)和循环伏安法(CV)研究修饰电极的电化学行为差异。差分脉冲伏安法(DPV)用于区别色氨酸(Trp)对映异构体,分离系数可达2.38。研究发现该修饰电极对L-Trp的DPV响应信号强于D-Trp,检测的线性范围为8.0×10~(-6)~4.0×10~(-3)mol/L,检出限(S/N=3)为5.0×10~(-6)mol/L。该方法简单、经济、快速,对发展其它手性化合物的检测方法提供了参考。     

Mass spectrometric characterization of peptides containing different oxidized tryptophan residues

The term reactive oxygen species refers to small molecules that can oxidize, for example, nearby proteins, especially cysteine, methionine, tryptophan, and tyrosine residues. Tryptophan oxidation is always irreversible in the cell and can yield several oxidation products, such as 5-hydroxy-tryptophan (5-HTP), oxindolylalanine (Oia), kynurenine (Kyn), and N-formyl-kynurenine (NFK). Because of the severe effects that oxidized tryptophan residues can have on proteins, there is a great need to develop generally applicable and highly sensitive techniques to identify the oxidized residue and the oxidation product. Here, the fragmentation behavior of synthetic peptides corresponding to sequences recently identified in three skeletal muscle proteins as containing oxidized tryptophan residues were studied using postsource decay and collision-induced dissociation (CID) in matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF)/TOF mass spectrometry (MS) and CID in an electrospray ionization (ESI) double quadrupole TOF-MS. For each sequence, a panel of five different peptides containing Trp, 5-HTP, Kyn, NFK, or Oia residue was studied. It was always possible to identify the modified positions by the y-series and also to distinguish the different oxidation products by characteristic fragment ions in the lower mass range by tandem MS. NFK- and Kyn-containing peptides displayed an intense signal at m/z 174.1, which could be useful in identifying accordingly modified peptides by a sensitive precursor ion scan. Most importantly, it was always possible to distinguish isomeric 5-HTP and Oia residues. In ESI- and MALDI-MS/MS, this was achieved by the signal intensity ratios of two signals obtained at m/z 130.1 and 146.1. In addition, high collision energy CID in the MALDI-TOF/TOF-MS also permitted the identification of these two isomeric residues by their v- and w-ions, respectively.