Stereochemistry Of Amino Acids Research Articles

Synthesis of Cyclotetrapeptides Analogues to Natural Products as Herbicides.

The synthesis of cyclotetrapeptides analogues of the natural products tentoxin and versicotide D was achieved in good yield by solid phase peptide synthesis (SPPS) of their linear precursors and solution phase cyclization. All the cyclopeptides and several open precursors were evaluated as herbicides. Five cyclopeptides and five lineal peptides showed a significant inhibition (>70%) of Ryegrass seed's radicle growth at 67 μg/mL. The evaluation at lower concentrations (4-11 μM) indicates two cyclopeptides analogs of tentoxin, which present one (N-Methyl-d-Phe), and two N-MeAA (N-Methyl-Ala and N-Methyl-Phe), respectively, as the most active of them, showing remarkable phytotoxic activity. In two cases, the open precursors are as active as their corresponding cyclopeptide. However, many linear peptides are inactive and their cyclization derivatives showed herbicidal activity. In addition, two cyclopeptide analogues of versicotide D showed more improved activity than the natural product. The results indicate that the peptide sequence, the amino acid stereochemistry and the presence of N-methyl group have important influence on the phytotoxic activity. Moreover, several compounds could be considered as lead candidates in the development of bioherbicides.

Antimicrobial and antitumor activity of peptidomimetics synthesized from amino acids

Thirteen cationic peptidomimetics derived from amino acids bearing an alkyl or ethynylphenyl moiety that mimic the structure of cationic antibacterial peptides were designed and synthesized using a simple coupling reaction of an amino acid with a substituted amine. Antibacterial activities of the resulting peptidomimetics against drug-sensitive bacteria, such as Gram-positive Staphylococcus aureus (S. aureus) and Bacillus subtilis, Gram-negative Escherichia coli (E. coli) and Salmonella enterica, and a drug-resistant bacterium, methicillin-resistant S. aureus (MRSA), were systematically evaluated. Most peptidomimetics show significant broad-spectrum antibacterial activity. A-L-Iso-C12 (isoleucine derivative bearing a dodecyl moiety) show MICs of 2.5 μg/mL against S. aureus and 4 μg/mL against MRSA and A-L-Val-C12 (valine derivative bearing a dodecyl moiety) show MICs of 1.67 μg/mL against E. coli and 8.3 μg/mL against MRSA. A-L-Val-C12 showed low cytotoxicity toward L929 cells in comparison with SGC 7901 cells, indicating tumor-directed killing by peptidomimetics while avoiding toxicity to normal cells. The influences of type of amino acid and substituent, length of substituent, and stereochemistry of amino acids on antibacterial activity and cytotoxicity of peptidomimetics were systematically investigated. The results indicate that this series of cationic peptidomimetics derived from amino acids display antitumor activity and may be useful for treatment of bacterial infections.

Modulation of physical properties of organic cocrystals by amino acid chirality

Amino acid chirality plays an important role in conveying directionality and specificity to their supramolecular organization. However, the impact of enantiopure and racemic amino acids on the favorable packing and macroscopic properties of organic cocrystals with nonchiral coformers is poorly understood. Herein, we performed a systematic study of the effect of chirality on the macroscopic properties of acetylated alanine (AcA) single crystals and cocrystals with a nonchiral photo-sensitive bipyridine derivative (BPE). Cocrystallization with BPE produced a marked morphology transition that improved the supramolecular chirality, thermal stability and mechanical strength of AcA crystals. The distinct supramolecular packing modes were analyzed by X-ray crystallography. The highest rigidity was observed for BPE/dl-AcA, while BPE/d-AcA and BPE/l-AcA crystals exhibited higher efficiency of photo-induced emission for fluorescent imprinting, as well as significantly higher piezoelectricity. This work provides a striking illustration that subtle differences in amino acid stereochemistry translate into tunable macroscopic properties of organic cocrystals for future applications in rigid solids, fluorescent imprinting, and energy harvesting.

A Bottom-Up Approach To Preserve Thioamide Residue Stereochemistry during Fmoc Solid-Phase Peptide Synthesis.

Thioamides are useful biophysical probes for the study of peptide structure and folding. The α-C stereochemistry of thioamide amino acids, however, is easily epimerized during solid-phase peptide synthesis (SPPS), which limits the sequence space that is available to thioamide incorporation. This work demonstrates that the α-C stereochemistry of thioamides can be reversibly protected in a manner that is compatible with the standard methodology of SPPS to enable the facile implementation of thioamide probes.

Effect of Linker Stereochemistry on the Activity of Indolinobenzodiazepine Containing Antibody-Drug Conjugates (ADCs).

Antibody-drug conjugates (ADCs) that incorporate potent indolinobenzodiazepine DNA alkylators as the payload component are currently undergoing clinical evaluation. In one ADC design, the payload molecules are linked to the antibody through a peptidase-labile l-Ala-l-Ala linker. In order to determine the role of amino acid stereochemistry on antitumor activity and tolerability, we incorporated l- and d-alanyl groups in the dipeptide, synthesized all four diastereomers, and prepared and tested the corresponding ADCs. Results of our preclinical evaluation showed that the l-Ala-l-Ala configuration provided the ADC with the highest therapeutic index (antitumor activity vs toxicity).

18F-Branched-Chain Amino Acids: Structure-Activity Relationships and PET Imaging Potential.

The large, neutral L-type amino acid transporters (LAT1-LAT4) are sodium-independent transporters that are widely distributed throughout the body. LAT expression levels are increased in many types of cancer, and their expression increases as cancers progress, leading to high expression levels in high-grade tumors and metastases. Because of the key role and overexpression of LAT in many types of cancer, radiolabeled LAT substrates are promising candidates for nuclear imaging of malignancies that are not well revealed by conventional radiotracers. The goal of this study was to examine the structure-activity relationships of a series of 18F-labeled amino acids that were predicted to be substrates of the LAT transport system. Methods: Using a photocatalytic radical fluorination, we prepared a series of 11 fluorinated branched-chain amino acids and evaluated them and their nonfluorinated parents in a cell-based LAT affinity assay. We radiofluorinated selected branched-chain amino acids via the same radical fluorination reaction and evaluated tumor uptake in U-87 glioma xenograft-bearing mice. Results: Structure-activity relationship trends observed in a LAT affinity assay were maintained in further in vitro studies, as well as in vivo using a U-87 xenograft model. LAT1 uptake was tolerant of fluorinated amino acid stereochemistry and chain length. PET imaging and biodistribution studies showed that the tracer (S)-5-18F-fluorohomoleucine had rapid tumor uptake, favorable in vivo kinetics, and good stability. Conclusion: By using an in vitro affinity assay, we could predict LAT-mediated cancer cell uptake in a panel of fluorinated amino acids. These predictions were consistent when applied to different cell lines and murine tumor models, and several new tracers may be suitable for further development as oncologic PET imaging agents.

Evolution of the genetic code based on conservative changes of codons, amino acids, and aminoacyl tRNA synthetases

The genetic code, as arranged in the standard tabular form, displays a non-random structure relating to the characteristics of the amino acids. An alternative arrangement can be made by organizing the code according to aminoacyl-tRNA synthetases (aaRSs), codons, and reverse complement codons, which illuminates a coevolutionary process that led to the contemporary genetic code. As amino acids were added to the genetic code, they were recognized by aaRSs that interact with stereochemically similar amino acids. Single nucleotide changes in the codons and anticodons were favored over more extensive changes, such that there was a logical stepwise progression in the evolution of the genetic code. The model presented traces the evolution of the genetic code accounting for these steps. Amino acid frequencies in ancient proteins and the preponderance of GNN codons in mRNAs for ancient proteins indicate that the genetic code began with alanine, aspartate, glutamate, glycine, and valine, with alanine being in the highest proportions. In addition to being consistent in terms of conservative changes in codon nucleotides, the model also is consistent with respect to aaRS classes, aaRS attachment to the tRNA, amino acid stereochemistry, and to a large extent with amino acid physicochemistry, and biochemical pathways.

A Universal HPLC-MS Method to Determine the Stereochemistry of Common and Unusual Amino Acids.

The determination of the stereochemistry of common and unusual amino acids is important in food chemistry, archeology, medicine, and life sciences including such diverse areas as marine biology and extraterrestrial chemistry and has greatly contributed to our current knowledge in these fields.To determine the stereochemistry of amino acids, many chromatographic methods have been developed and refined over the last decades. Here we describe a state-of-the-art indirect chromatography-based LC-MS method. Diastereomers were formed from amino acids that were reacted with chiral derivatizing agents such as Marfey's reagent (FDAA), GITC, S-NIFE, and OPA-IBLC and separated on a reversed phase column using mass spectrometry compatible buffers.

Aza-proline effectively mimics l-proline stereochemistry in triple helical collagen.

The prevalence of l-amino acids in biomolecules has been shown to have teleological importance in biomolecular structure and self-assembly. Recently, biophysical studies have demonstrated that natural l-amino acids can be replaced with non-natural achiral aza-amino acids in folded protein structures such as triple helical collagen. However, the structural consequences of achiral aza-amino acid incorporation has not been elucidated in the context of any relevant folded biomolecule. Herein, we use X-ray crystallography to provide the first atomic resolution crystal structure of an achiral aza-amino acid residue embedded within a folded protein structure, definitively illustrating that achiral aza-proline has the capacity to effectively mimic the stereochemistry of natural amino acids within the context of triple helical collagen. We further corroborate this finding with density functional theory computational analysis showing that the natural l-amino acid stereochemistry for aza-proline is energetically favored when arranged in the aza-proline-hydroxyproline-glycine motif. In addition to providing fundamental insight into peptide and protein structure, the incorporation of achiral stereochemical mimics such as aza-amino acids could have far reaching impacts in areas ranging from synthetic materials to drug design.

Simplification of FDLA Pre-Column Derivatization for LC/MS/MS Toward Separation and Detection of d,l-Amino Acids

Chiral chromatography is a sensitive technique used to separate l- and d-amino acids. Marfey’s reagent (1-fluoro-2,4-dinitrophenyl-5-l-alaninamide, FDAA) has been used as a chiral derivatization reagent to determine amino acid stereochemistry. Replacement of alanylamide in this reagent with leucylamide resulted in the derivative 1-fluoro-2,4-dinitrophenyl-5-l-leucinamide (FDLA), which proved a superior chiral derivatization reagent for the separation of d,l-amino acids due to the improved LC/MS measurement sensitivity. However, FDLA derivatization requires alkaline conditions, achieved with the use of NaHCO3, which necessitates an additional desalting step (e.g., liquid–liquid extraction) before quantitative analysis using LC/MS/MS. To establish a simplified LC/MS/MS measurement method, solid NaHCO3 was replaced with volatile triethylamine (TEA). The 30-min derivatization using FDLA under alkaline conditions with TEA at room temperature allowed for exclusion of the desalting step from the FDLA pre-column derivatization. Furthermore, using TEA, larger peak areas and more effective detection of hydrophilic amino acids could be achieved.

Functional group and stereochemical requirements for substrate binding by ghrelin O-acyltransferase revealed by unnatural amino acid incorporation

Ghrelin is a small peptide hormone that undergoes a unique posttranslational modification, serine octanoylation, to play its physiological roles in processes including hunger signaling and glucose metabolism. Ghrelin O-acyltransferase (GOAT) catalyzes this posttranslational modification, which is essential for ghrelin to bind and activate its cognate GHS-R1a receptor. Inhibition of GOAT offers a potential avenue for modulating ghrelin signaling for therapeutic effect. Defining the molecular characteristics of ghrelin that lead to binding and recognition by GOAT will facilitate the development and optimization of GOAT inhibitors. We show that small peptide mimics of ghrelin substituted with 2,3-diaminopropanoic acid in place of the serine at the site of octanoylation act as submicromolar inhibitors of GOAT. Using these chemically modified analogs of desacyl ghrelin, we define key functional groups within the N-terminal sequence of ghrelin essential for binding to GOAT and determine GOAT’s tolerance to backbone methylations and altered amino acid stereochemistry within ghrelin. Our study provides a structure-activity analysis of ghrelin binding to GOAT that expands upon activity-based investigations of ghrelin recognition and establishes a new class of potent substrate-mimetic GOAT inhibitors for further investigation and therapeutic interventions targeting ghrelin signaling.

2D Chiroptical Nanostructures for High‐Performance Photooxidants

AbstractModulation of the chirality of solid‐like nanoscale membranous structures used as selective photooxidants is an important goal of chemical and materials science. Here, the fabrication of a chiral plasmonic nanoparticle monolayer film which is a highly selective photooxidant under circularly polarized light (CPL) in the visible‐light region is reported. The chiroptical activity of the film can be controlled by altering the amount and stereochemistry of amino acids. The experiments disclose that this stable and reusable catalyst is active in the selective oxidation of glucose enantiomers and CPL of opposite polarization gives around 10.3‐fold increase in conversion rates. The results reveal that the handedness of polarized light dominates the catalytic activity of the chiral film. It is demonstrated that the specific chiral binding of the amino acid ligands and the local field enhancement in the light‐limited regime regulates the selective photocatalytic performance, as confirmed by first‐principles density functional theory and physical field simulations. With the catalyst's signature ability for chiral recognition and switching of handedness of polarized light, the discovery provides a foundation for designing and tailoring chiral inorganic photooxidants. This research also sets an example for the development of light–matter interactions and polarized optics.

Lipovelutibols A-D: Cytotoxic Lipopeptaibols from the Himalayan Cold Habitat Fungus Trichoderma velutinum.

Four novel lipovelutibols A (1), B (2), C (3), and D (4) containing six amino acid residues with leucinol at the C-terminus and a fatty acyl moiety (n-octanoyl) at its N-terminus were isolated from the psychrotrophic fungus Trichoderma velutinum collected from the Himalayan cold habitat. The structures (1-4) were determined by NMR and MS/MS, and the stereochemistry of amino acids by Marfey's method. Lipopeptaibols 2 and 4 were found to contain d-isovaline, a nonproteinogenic amino acid, but lacked α-aminoisobutyric acid, characteristic of peptaibols. Cytotoxic activity of 2 and 4 was observed against HL-60, LS180, MDA-MB-231, and A549 cancer cell lines.

Controlled enzymatic stability and release characteristics of supramolecular chiral peptide amphiphile nanofiber gels

Supramolecular bioarchitectures formed by assembly of achiral or chiral building blocks play important roles in various biochemical processes. Stereochemistry of amino acids is important for structural organization of peptide and protein assemblies and structure-microenvironment interactions. In this study, oppositely charged peptide amphiphile (PA) molecules with L-, D- and mixture of l- and d-amino acid conformations are coassembled into supramolecular nanofibers and formed self-supporting gels at pH 7.4 in water. The enzymatic stability of the PA nanofiber gels was studied in the presence of proteinase K enzyme, which digest a broad spectrum of proteins and peptides. The structural changes on the chiral PA nanofibers were also analyzed at different time periods in the presence of enzymatic activity. Controlled release of a model cargo molecule through the chiral PA nanofiber gels was monitored. The diffusivity parameters were measured for all gel systems. Release characteristics and the enzymatic stability of the peptide nanofiber gels were modulated depending on organization of the chiral PA molecules within the supramolecular assemblies.

D-Amino Acid Scan of Two Small Proteins.

A "D-scan" of two small proteins, the disulfide-rich Ecballium elaterium trypsin inhibitor II (EETI-II) and a minimized Z domain of protein A (Z33), is reported. For each protein, the stereochemistry of one amino acid at a time was inverted to generate a series of diastereomers. In much the same way an alanine scan determines necessary residues for protein function, the D-scan elucidated the critical stereocenters of the 30-residue EETI-II and the 33-residue Z33. The folding properties and activity of each variant were investigated. A total of 24 out of 30 EETI-II D-scan analogues folded to give a three-disulfide product. Of the 24 variants that folded, half were high-affinity trypsin inhibitors, and three were as active as the wild type (WT). Of these 12 active variants, most were substantially less stable to reduction than WT EETI-II (WT first reduction potential -270.0 ± 1.5 mV, WT second reduction potential -307.2 ± 1.1 mV). Similarly, ten Z33 analogues retained high binding affinity to IgG (KD < 250 nM, WT: 24 ± 1 nM) and 12 additional analogues had reduced but appreciable IgG binding affinity (KD between 250 nM and 2.5 μM). As with EETI-II, most Z33 analogues were substantially less stable than the WT (ΔG(H2O, 263 K) = 2.4 ± 1.2 kcal/mol). Collectively, our findings show that the D-scan is powerful new strategy for studying how the stereochemistry of amino acids affects the structure and function of proteins.

Iron catalysts diversify amino acids and peptides

To create peptides with diverse types of bioactivity, microorganisms use multienzyme complexes called nonribosomal peptide synthetases (NRPSs). For example, bacteria make the antibiotic vancomycin this way. Iron-based enzymes in NRPSs oxidize and modify amino acids both before and after the complexes assemble the amino acids into peptides. A new technique enables chemists to diversify amino acids and peptides the way that NRPSs do. The approach, its developers say, could make it easier to discover new peptide-based therapeutics, dozens of which are already on the market or in testing. Chemists aren’t as good at diversifying peptides as microbes are. Researchers often must synthesize peptides with modified amino acids from scratch, a laborious and time-consuming process. There are a few ways to oxidize amino acids to functionalize the molecules, but these techniques are frequently difficult, sometimes alter amino acid stereochemistry, and have limited ability to modify amino acids already in peptides. M.

Peptide Bond Formation in Water Mediated by Carbon Disulfide.

Demonstrating plausible nonenzymatic polymerization mechanisms for prebiotic monomers represents a fundamental goal in prebiotic chemistry. While a great deal is now known about the potentially prebiotic synthesis of amino acids, our understanding of abiogenic polymerization processes to form polypeptides is less well developed. Here, we show that carbon disulfide (CS2), a component of volcanic emission and sulfide mineral weathering, and a widely used synthetic reagent and solvent, promotes peptide bond formation in modest yields (up to ∼20%) from α-amino acids under mild aqueous conditions. Exposure of a variety of α-amino acids to CS2 initially yields aminoacyl dithiocarbamates, which in turn generate reactive 2-thiono-5-oxazolidone intermediates, the thio analogues of N-carboxyanhydrides. Along with peptides, thiourea and thiohydantoin species are produced. Amino acid stereochemistry was preserved in the formation of peptides. Our findings reveal that CS2 could contribute to peptide bond formation, and possibly other condensation reactions, in abiogenic settings.

Gas chromatographic separation of stereoisomers of non-protein amino acids on modified γ-cyclodextrin stationary phase

Stereoisomers (enantiomers and diastereoisomers) of synthetic, non-protein amino acids comprising α-, β-, and γ-amino acids, including α,α-dialkyl amino acids, were converted into the respective N-trifluoroacetyl-O-methyl esters and analyzed and resolved by gas chromatography (GC) on a commercial fused silica capillary column coated with the chiral stationary phase octakis(3-O-butyryl-2,6-di-O-pentyl)-γ-cyclodextrin. This column is marketed under the trade name Lipodex® E. Chromatograms, retention times, and a chart displaying the retention times of approximately 40 stereoisomers of amino acids are presented. With few exceptions, baseline or almost baseline resolution was achieved for enantiomers and diastereoisomers. The chromatographic method presented is considered to be highly suitable for the elucidation of the stereochemistry of non-protein amino acids, for example in natural products, and for evaluating the enantiopurity of genetically non-coded amino acids used for the synthesis and design of conformationally tailored peptides. The method is applicable to extraterrestrial materials or can be used in experimental work related to abiotic syntheses or enantioselective destruction and amplification of amino acids.

Abstract 1618: New peptide-linked anilino-maytansinoid antibody-drug conjugates (ADCs) for the treatment of cancer

Abstract A number of ADCs consisting of a maytansinoid cytotoxic agent linked to an antibody via a cleavable disulfide linker or a non-cleavable thioether linker are in the clinic. In preclinical models, antibody-maytansinoid conjugates (AMCs) utilizing a cleavable disulfide linker have been shown to be able to kill both the targeted antigen-positive (Ag+) cancer cells and also adjacent Ag- “bystander” cancer cells because of intra-cellular generation of maytansinoid catabolites that can travel out of the Ag+ cells, into adjacent Ag- cells, and kill these cells when they divide. Such bystander killing of Ag- cancer cells can be advantageous for some tumor types, such as those with heterogeneous target expression on the cancer cells. We thus developed a new dipeptide linker designed to promote bystander killing more efficiently than current disulfide linkers. It is used to attach an aniline-bearing maytansinoid to the targeting antibody. To determine the effect of amino acid stereochemistry on the therapeutic index, dipeptide-anilino AMCs (dpa-AMCs) were prepared with the four possible L- and D-alanine configurations using an anti-EGFR antibody. These were compared to a dpa-AMC containing the L-Val-L-Cit dipeptide, which is a commonly utilized dipeptide for ADC linkage. Dipeptide stereochemistry had a significant effect on the in vitro potency and bystander killing activity of the AMCs. Based on the results, the three most potent designs - those bearing the L-Ala-L-Ala, D-Ala-L-Ala, and L-Val-L-Cit peptides - were further investigated. In tolerability experiments in mice, with AMC dosing based on linked maytansinoid, the MTDs of the D-Ala-L-Ala dpa-AMCs and a disulfide linked control AMC were both approximately 1.4 mg/kg, while the L-Val-L-Cit and L-Ala-L-Ala dpa-AMCs were not as well tolerated. The AMC with the disulfide linker and the three most potent dpa-AMCs had similar in vivo efficacy in tumor xenograft models in mice where the antigen was expressed homogeneously. The D-Ala-L-Ala dpa-AMC however was selected as the lead based on its favorable MTD and because its anti-CanAg conjugate had 2-3 fold greater efficacy in vivo than a disulfide linked anti-CanAg AMC in a HT-29 tumor model, where the antigen is expressed heterogeneously. Cellular processing studies revealed that the anti-CanAg D-Ala-L-Ala dpa-AMC produced a unique, highly potent anilino-maytansinoid catabolite that can diffuse into, and kill, bystander cells. In conclusion, we have developed a promising new type of maytansinoid ADC, one that provides a high degree of bystander killing, improved activity in a heterogeneous tumor model in vivo, and a different mechanism of cytotoxic catabolite release than current AMC designs. Citation Format: Wayne C. Widdison, Joe Ponte, Jennifer Coccia, Yulius Setiady, Ling Dong, Anja Skaletskaya, Nathan Fishkin, Yelena Kovtun, Rui Wu, Rajeeva Singh, Luke Harris, Greg Jones, Leanne Lanieri, Erin Maloney, Charlene Audette, Andre Dandeneau, Ravi Chari, Juliet Costoplus, Karen Veale, Sharon Wilhelm. New peptide-linked anilino-maytansinoid antibody-drug conjugates (ADCs) for the treatment of cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1618. doi:10.1158/1538-7445.AM2014-1618

Determination and stereochemistry of proteinogenic and non-proteinogenic amino acids in Saudi Arabian date fruits.

Whereas an abundance of literature is available on the occurrence of common proteinogenic amino acids (AAs) in edible fruits of the date palm (Phoenix dactylifera L.), recent reports on non-proteinogenic (non-coded) AAs and amino components are scarce. With emphasis on these components we have analyzed total hydrolysates of twelve cultivars of date fruits using automated ion-exchange chromatography, HPLC employing a fluorescent aminoquinolyl label, and GC-MS of total hydrolysates using the chiral stationary phases Chirasil(®)-L-Val and Lipodex(®) E. Besides common proteinogenic AAs, relatively large amounts of the following non-proteinogenic amino acids were detected: (2S,5R)-5-hydroxypipecolic acid (1.4-4.0 g/kg dry matter, DM), 1-aminocyclopropane-1-carboxylic acid (1.3-2.6 g/kg DM), γ-amino-n-butyric acid (0.5-1.2 g/kg DM), (2S,4R)-4-hydroxyproline (130-230 mg/kg DM), L-pipecolic acid (40-140 mg/kg DM), and 2-aminoethanol (40-160 mg/kg DM) as well as low or trace amounts (<70 mg/kg DM) of L-ornithine, 5-hydroxylysine, β-alanine, and in some samples (<20 mg/kg DM) of (S)-β-aminoisobutyric acid and (<10 mg/kg DM) L-allo-isoleucine. In one date fruit, traces of α-aminoadipic acid could be determined. Enantiomeric analysis of 6 M DCl/D2O hydrolysates of AAs using chiral capillary gas chromatography-mass spectrometry revealed the presence of very low amounts of D-Ala, D-Asp, D-Glu, D-Ser and D-Phe (1.2-0.4%, relative to the corresponding L-enantiomers), besides traces (0.2-1%) of other D-AAs. The possible relevance of non-proteinogenic amino acids in date fruits is briefly addressed.