Pure Amino Acids Research Articles

Enhanced hydrate formation under mild conditions using a novel spiral‐agitated reactor

AbstractHydrate‐based solidified natural gas (SNG) technology provides a promising approach to store and transport natural gas, but demanding formation conditions and low methane storage capacity limit its application. Here, we presented a novel spiral‐agitated reactor, and hydrate formation in pure water and amino acid systems was evaluated. It is worth to highlight that spiral agitation significantly enhances initial hydrate grow kinetics, and satisfied methane uptake of 134.9 V/V was obtained under a mild condition (4.3 MPa, 275.15 K, and 30 rpm). Impressively, when amino acids were introduced, late hydrate growth was greatly improved because of secondary uptake, and a large methane uptake (145.97 V/V) was obtained under a milder condition (3.8 MPa, 275.15 K, and 60 rpm), which increases by 82.97% comparing to that in pure water systems. These findings provide a new insight (synergistic effect of spiral agitation and amino acids) on enhanced hydrate production under extremely mild conditions.

Average and Standard Deviation of the Error Function for Random Genetic Codes with Standard Stop Codons.

The origin of the genetic code has been attributed in part to an accidental assignment of codons to amino acids. Although several lines of evidence indicate the subsequent expansion and improvement of the genetic code, the hypothesis of Francis Crick concerning a frozen accident occurring at the early stage of genetic code evolution is still widely accepted. Considering Crick's hypothesis, mathematical descriptions of hypothetical scenarios involving a huge number of possible coexisting random genetic codes could be very important to explain the origin and evolution of a selected genetic code. This work aims to contribute in this regard, that is, it provides a theoretical framework in which statistical parameters of error functions are calculated. Given a genetic code and an amino acid property, the functional code robustness is estimated by means of a known error function. In this work, using analytical calculations, general expressions for the average and standard deviation of the error function distributions of completely random codes with standard stop codons were obtained. As a possible biological application of these results, any set of amino acids and any pure or mixed amino acid properties can be used in the calculations, such that, in case of having to select a set of amino acids to create a genetic code, possible advantages of natural selection of the genetic codes could be discussed.

Comparative study of different chiral ligands for dynamic kinetic resolution of amino acids.

Dynamic kinetic resolution (DKR) of unprotected amino acids (AAs), via intermediate formation of Ni(II) complexes, is currently a leading methodology for preparation of natural and tailor-made AAs in enantiomerically pure form. In this work, we conduct a comparative case study of synthetic performance of four different ligands in DKR of six AAs representing aryl-, benzyl-, alkyl-, and long alkyl-type derivatives. The results of this study allow for rational selection of ligand/AA type to develop a practical procedure for preparation of target enantiomerically pure AAs.

Synthesis of Enantiopure Unnatural Amino Acids by Metallaphotoredox Catalysis.

We describe herein a two-step process for the conversion of serine to a wide array of optically pure unnatural amino acids. This method utilizes a photocatalytic cross-electrophile coupling between a bromoalkyl intermediate and a diverse set of aryl halides to produce artificial analogues of phenylalanine, tryptophan, and histidine. The reaction is tolerant of a broad range of functionalities and can be leveraged toward the scalable synthesis of valuable pharmaceutical scaffolds via flow technology.

Collagen peptide provides Streptomyces coelicolor CGMCC 4.7172 with abundant precursors for enhancing undecylprodigiosin production

Effective and ecofriendly converting biomass to chemicals is important for sustainable engineering based on the foreseeable shortage of fossil resources. Undecylprodigiosin (UP) is a promising antibiotic, but the direct feeding of pure precursor amino acids makes it costly for large-scale production. Here, collagen peptide (CP), a renewable animal-derived biomass contains abundant precursor amino acids of UP. CP can act as carbon and nitrogen source for the growth of Streptomyces coelicolor CGMCC 4.7172. The plant biomasses including soybean meal, wheat bran, and malt extract were unsuitable for UP prodution. However, 365.40 µg/L UP was detected after 24 h in the media containing CP, and its highest concentration reached 1198.01 µg/L. UP was also detected in the media containing meat hydrolysates of domestic animals, but its initial production time was delayed, and final concentration was lower than that in the medium containing CP only. Compared the fermentation performances of CP and other proteins, CP has a special superiority for UP production. These results revealed that UP biosynthesis may be dependent on amino acid availability of substrates and CP is beneficial for UP production because of its specific amino acid composition.Graphical abstract

The Effect of Noise in Raman Spectra on the Reconstruction of the Concentration of Amino Acids in the Mixture by Multivariate Curve Resolution (MCR) Analysis

Changes in the concentration of free amino acids in biological tissues is a sign of impaired protein metabolism in patients with cancer. Recently, Raman spectroscopy has been used for early diagnostics of oncological diseases. The concentrations of individual components of biological tissue (for instance, the concentrations of amino acids) can be obtained by decomposing the tissue Raman spectrum. This study was designed to evaluate the effect of noise in the Raman spectra of individual amino acids on the result of the decomposition of the spectra of an amino acid mixture. As a decomposition method, we used Multivariate Curve Resolution-Alternating Least Squares (MCR–ALS) analysis and investigate experimental Raman spectra of amino acids and mathematically simulated Raman spectra of amino acid mixtures. Noise with different signal-to-noise ratios (SNR) was artificially added to both the experimental spectra of pure amino acids and the spectra of the mixtures. Concentration values for each amino acid obtained as a result of applying the MCR–ALS analysis have been compared with the corresponding true values and the correlation coefficients have been calculated. The results show a less pronounced negative effect of noise in the case when the spectra of pure amino acids (which were used as a basis for the MCR–ALS analysis) are noisy, and a more pronounced negative effect when the spectrum of the mixture is noisy. The accuracy of reconstruction of an amino acid is also negatively affected by strong background fluorescence in the amino acid spectrum. Moreover, the results indicate that using the basis spectra with a high SNR (SNR = 5) makes it possible to successfully estimate the amino acid concentrations in a mixture even when the Raman spectrum of the mixture is noisy and has a low SNR (SNR < 5).

Scale-up economics for cultured meat.

This analysis examines the potential of “cultured meat” products made from edible animal cell culture to measurably displace the global consumption of conventional meat. Recognizing that the scalability of such products must in turn depend on the scale and process intensity of animal cell production, this study draws on technoeconomic analysis perspectives in industrial fermentation and upstream biopharmaceuticals to assess the extent to which animal cell culture could be scaled like a fermentation process. Low growth rate, metabolic inefficiency, catabolite inhibition, and shear‐induced cell damage will all limit practical bioreactor volume and attainable cell density. Equipment and facilities with adequate microbial contamination safeguards have high capital costs. The projected costs of suitably pure amino acids and protein growth factors are also high. The replacement of amino‐acid media with plant protein hydrolysates is discussed and requires further study. Capital‐ and operating‐cost analyses of conceptual cell‐mass production facilities indicate economics that would likely preclude the affordability of their products as food. The analysis concludes that metabolic efficiency enhancements and the development of low‐cost media from plant hydrolysates are both necessary but insufficient conditions for displacement of conventional meat by cultured meat.

Water Microdroplets Allow Spontaneously Abiotic Production of Peptides.

The chemistry of abiotic synthesis of peptides in the context of their prebiotic origins is a continuing challenge that arises from thermodynamic and kinetic constraints in aqueous media. Here we reported a strategy of microdroplets' mass spectrometry for peptide bonds formed from pure amino acids or a mixture in the presence of phosphoric acids in aqueous microdroplets. In contrast to bulk experiments, the condensation reactions proceed spontaneously under ambient conditions. The microdroplet gave a negative free-energy change (ΔG ∼ -1.1 kcal/mol), and product yields of ∼75% were obtained at the scale of a few milliseconds. Experiments in which nebulization gas pressure and external charge were varied established dependence of peptide production on the droplet size that has a high surface-to-volume ratio. It is concluded that the condensation reactions occurred at or near the air-water interfaces of microdroplets. This aqueous microdroplets approach also provides a route for chemistry synthesis in the prebiotic era.

Louis Isaac Woolf (24 April 1919 – 7 February 2021)

Professor Emeritus Louis Woolf died aged 101 on Sunday, 7 February 2021, in Vancouver, British Columbia. He is best known for his pioneering work conceiving and developing the first dietary treatment for phenylketonuria (PKU) based on a phenylalanine – a depleted hydrolysate of milk protein. His idea came from a ‘light bulb’ moment at a biochemistry meeting.Louis joined the Biochemical Society in May 1949 and continued until his death. He was thereby one of the longest ever serving members of the Society.He was born in London, the third child of Jewish parents from northern Romania. In 1938 he gained scholarships to study for a degree in chemistry at University College London (UCL) achieving First Class Honours and then a PhD. In 1939, at the outbreak of World War II, he was evacuated to Aberystwyth in Wales, along with the rest of UCL, to complete his degrees. There he met his future wife Frances Mary Richards.In 1947 he secured a post at Great Ormond Street Hospital (GOSH) to research tyrosine metabolism in premature babies. His first publication in a 1950 issue of the Biochemical Journal described this. Included in his chromatography studies were patients with PKU, then considered ‘untreatable’. He had postulated that their severe learning difficulties arose either from their abnormally raised blood phenylalanine concentrations or its toxic metabolite phenylacetic acid. He presented his investigations on the latter at the 1951 Biochemical Society Annual General Meeting in London. He wondered, could PKU patients be treated by lowering their concentration of phenylalanine with an artificial, low phenylalanine diet with added nutrients to make it a complete food? A protein substitute of pure amino acids was then extremely expensive. Fortuitously he went to a Biochemical Society meeting at which an economical growth medium for the microbiological assay of amino acids in protein was described. Phenylalanine and aromatic amino acids were removed from an acid hydrolysate of protein by filtration through charcoal. Louis knew that an acid hydrolysate of the milk protein, casein, was available from Allen and Hanbury, where he had worked, and could provide the basis for his dietary concept. Louis was unable to persuade paediatricians at GOSH to trial this. More receptive was a German paediatrician, Horst Bickel, visiting from his post in Birmingham, who enquired whether Louis could think of a way to treat PKU. Whilst sceptical of Louis’ idea, Bickel successfully treated a 2-year-old girl with PKU in Birmingham utilizing Louis’ method for producing a liquid food low in phenylalanine content. This was a world first and a lasting legacy.Louis moved to Oxford in 1958 to continue research into PKU. It is less well known that, since his time at GOSH, Louis had been convinced that newborn screening for PKU would improve outcomes by enabling earlier dietary therapy. Urine testing was a simple and non-invasive way and he and Senior Medical Officer in Public Health, Dr Nancy Gibbs, trialled a urine screening programme aimed at detecting all cases of PKU in a cohort of babies in Cardiff, Wales, from 1958 to 1959 – another world first which was partially successful. By 1968, with experience from other trials in other UK countries, it was apparent that urine detection in new-borns was insufficiently reliable and blood analysis became the recommendation with the heel prick test we are now so familiar with.Louis’ published work and presentations had become known internationally. In 1968 Dr William Gibson offered him a post as associate professor at the University of British Columbia (UBC). He was promoted to professor 6 years later in 1974. He published extensively, with over 120 papers to his name, a book on renal tubular dysfunction and contributions to books, conferences and supervision of many research students. He retired in 1984 after a 16-year teaching and research career at UBC.A shy and modest man, he was devoted to his family. His wife Frances died in 1991 and Louis is survived by his only daughter Lesley, grandsons Benjamin and Oliver, two great-grandchildren, Graham and Willow, and his youngest brother, Henry. He was beautifully spoken in a refined, old-fashioned British way with an astonishing memory to the end. Generous to people who criticized him, he quietly stood his ground, recognizing that valid debate is integral to scientific discovery. And – like many another innovative scientist – it is in this way that he triumphed over sceptical adversity to leave a legacy in pioneering the successful treatment of PKU.

Bioleaching of Gold from Silicate Ore by Macrococcus caseolyticus and Acinetobacter calcoaceticus: Effect of Medium, Amino Acids and Growth Supernatant

The aims of this work were to study the gold leaching by the isolated bacteria from silicate ore. Three strains were isolated and identified as Macrococcus caseolyticus, Acinetobacter calcoaceticus, and Bacillus sp. MBEA40. However, only M. caseolyticus and A. calcoaceticus were capable of gold bioleaching. In order to examine only the effect of microorganisms involved in the gold bioleaching process, minimal medium and ethanol mineral salt medium without amino acids were used for culturing M. caseolyticus and A. calcoaceticus, respectively. The result showed that the growth supernatant (in the absence of microorganisms) of both strains might be more suitable to leaching gold from ore than leaching by microorganisms (in the presence of microorganisms) directly. This might be due to the fact that there is no interference of gold absorption and metal toxicity in microorganisms in the long-term operation. The result also confirmed that amino acids/peptides/proteins produced by microorganisms might be involved in gold bioleaching, as shown in the high-performance liquid chromatography (HPLC) results. The Fourier transform infrared spectroscopy (FTIR) study also found that amine groups and carboxylic groups played important roles in gold bioleaching by M. caseolyticus and A. calcoaceticus. In addition, the bioleaching process had significantly higher gold leaching than mixed pure amino acids due to the growth supernatant containing mixed amino acids/peptides/proteins and other compounds. Therefore, the growth supernatant of M. caseolyticus and A. calcoaceticus can be applied in gold bioleaching under neutral pH conditions, which is considered to be a safe, not corrosive, and environmentally friendly leaching process. This study is also needed further study in order to increase the percentage of gold bioleaching and decrease times.

Enantioselective extraction of unprotected amino acids coupled with racemization

Scalable and economical methods for the production of optically pure amino acids, both natural and unnatural, are essential for their use as synthetic building blocks. Currently, enzymatic dynamic kinetic resolution (DKR) underpins some of the most effective processes. Here we report the development of enantioselective extraction coupled with racemization (EECR) for the chirality conversion of underivatized amino acids. In this process, the catalytic racemization of amino acids in a basic aqueous solution is coupled with the selective extraction of one enantiomer into an organic layer. Back-extraction from the organic layer to an acidic aqueous solution then completes the deracemization of the amino acid. The automation of the EECR process in a recycling flow reactor is also demonstrated. Continuous EECR is made possible by the sterically hindered chiral ketone extractant 5, which prevents the coextraction of the copper racemization catalyst because of its nonplanar geometry. Furthermore, the extractant 5 unexpectedly forms imines with amino acids faster and with greater enantioselectivity than less bulky derivatives, even though 5 cannot participate in intramolecular resonance-assisted hydrogen bonding. These features may allow EECR to challenge the preponderance of enzymatic DKR in the production of enantiomerically enriched amino acids.

L-alanine supplementation improves blood glucose level and biochemical indices in alloxan-induced diabetic rats.

Diabetes is a metabolic disorder whose complications are among the leading cause of death. In this study, the antidiabetic effect of L-alanine was tested in alloxan-induced diabetic rats. Thirty-five male albino Wistar rats were divided into five groups viz; Group I and II: nondiabetic and diabetic controls respectively; Group III and IV: 150 and 300mg/kg b.w. L-alanine treated, respectively; Group V: glibenclamide (0.5mg/kg b.w.) treated. Weight and blood glucose were monitored during the study, while liver and kidney functions, lipid profile, and antioxidant markers were examined at the end of the study. The outcomes indicate that 300mg/kg L-alanine resulted to a significant decrease (p<.05) in weight and blood glucose. L-alanine restored tissue antioxidants, kidney, and liver functions by improving important parameters. Histopathological studies showed the potential of L-alanine in regeneration of the islets of Langerhans. These findings suggest that L-alanine has an alleviating effect on alloxan-induced diabetes. PRACTICAL APPLICATIONS: Several medicinal plants have been tested for their antidiabetic potentials, however, the isolation of the active compounds from these plants for medicinal use is often challenging. Here, we present data that suggests the potential use of a pure and harmless amino acid compound (L-alanine) for the management of diabetes. L-alanine is readily available, cheap and can also be found in many foods we eat. Therefore, L-alanine may be taken by diabetic patients as a food supplement for the treatment/management of diabetes or taken as part of foods rich in the amino acid such as meat, poultry, fish, eggs, and dairy products.

Top-Down Characterization of an Antimicrobial Sanitizer, Leading From Quenchers of Efficacy to Mode of Action.

We developed a top-down strategy to characterize an antimicrobial, oxidizing sanitizer, which has diverse proposed applications including surface-sanitization of fresh foods, and with benefits for water resilience. The strategy involved finding quenchers of antimicrobial activity then antimicrobial mode of action, by identifying key chemical reaction partners starting from complex matrices, narrowing down reactivity to specific organic molecules within cells. The sanitizer electrolyzed-water (EW) retained partial fungicidal activity against the food-spoilage fungus Aspergillus niger at high levels of added soils (30–750 mg mL–1), commonly associated with harvested produce. Soil with high organic load (98 mg g–1) gave stronger EW inactivation. Marked inactivation by a complex organics mix (YEPD medium) was linked to its protein-rich components. Addition of pure proteins or amino acids (≤1 mg mL–1) fully suppressed EW activity. Mechanism was interrogated further with the yeast model, corroborating marked suppression of EW action by the amino acid methionine. Pre-culture with methionine increased resistance to EW, sodium hypochlorite, or chlorine-free ozonated water. Overexpression of methionine sulfoxide reductases (which reduce oxidized methionine) protected against EW. Fluoroprobe-based analyses indicated that methionine and cysteine inactivate free chlorine species in EW. Intracellular methionine oxidation can disturb cellular FeS-clusters and we showed that EW treatment impairs FeS-enzyme activity. The study establishes the value of a top-down approach for multi-level characterization of sanitizer efficacy and action. The results reveal proteins and amino acids as key quenchers of EW activity and, among the amino acids, the importance of methionine oxidation and FeS-cluster damage for antimicrobial mode-of-action.

N-Butanol production by Saccharomyces cerevisiae from protein-rich agro-industrial by-products.

n-Butanol is a renewable resource with a wide range of applications. Its physicochemical properties make it a potential substitute for gasoline. Saccharomyces cerevisiae can produce n-butanol via amino acid catabolic pathways, but the use of pure amino acids is economically unfeasible for large-scale production. The aim of this study was to optimize the production of n-butanol by S. cerevisiae from protein-rich agro-industrial by-products (sunflower and poultry offal meals). By-products were characterized according to their total protein and free amino acid contents and subjected to enzymatic hydrolysis. Protein hydrolysates were used as nitrogen sources for the production of n-butanol by S. cerevisiae, but only poultry offal meal hydrolysate (POMH) afforded detectable levels of n-butanol. Under optimized conditions (carbon/nitrogen ratio of 2 and working volume of 60%), 59.94mg/L of n-butanol was produced using POMH and glucose as substrates. The low-cost agro-industrial by-product showed great potential to be used in the production of n-butanol by S. cerevisiae. Other protein-rich residues may also find application in biofuel production by yeasts.

2-(Substituted amino)-8-azachromones from 4,6-Diaryl-2-pyridones: A Synthetic Strategy toward Compounds of Broad Structural Diversity.

3-Acetoacetyl-4,6-diaryl-2-pyridones are synthesized in three steps from chalcones and then condense with carbon disulfide to afford 8-azachromones containing a methylthio group at C2. This leaving group offers an entry point for the insertion of more complex moieties via nucleophilic substitution. For this purpose, N-nucleophiles are explored according to their positions in the Mayr's nucleophilicity scale (N parameter), and three main classes are distinguished depending on whether the substitution takes place from their neutral forms, from their deprotonated anionic forms, or under nucleophilic catalysis. A broad range of primary and secondary amines may be inserted by this method, including enantiomerically pure amino acids, enabling us to explore structural diversity.

Symmetry breaking in the solid state of 9,10-anthracene amino acid conjugates as seen by X-ray diffraction and NMR spectroscopy

Three novel structures of 9,10-anthracene amino acid conjugates have been determined by combination of single crystal and powder X-ray diffraction measurements, pseudopotential plane wave DFT optimizations and 13C solid state NMR spectroscopy, including GIPAW calculation of the NMR parameters. All three structures show anti-conformation of amino acid side chains attached to the anthracene unit. For compounds Ant–(CO–Phe-OMe)2, (1) and Ant–(CO–Gly-Phe-OMe)2 (2), anti-conformation is in accordance with nearly centrosymmetric crystallographic structures, while for Ant–(CO–Val-OMe)2 (3), anti-conformation is in accordance with approximate 2-fold molecular axis passing through the plane of anthracene unit. Centres of inversion in 1 and 2 are approximate due to the usage of optically pure amino acids. Rotation axis in 3 is approximate due to the displacement of molecules from crystallographic 2-fold axes present in tetragonal P41212 space group, resulting in a structure more accurate described in space group P212121.

A novel, enantioselective, thermostable recombinant hydantoinase to aid the synthesis of industrially valuable non-proteinogenic amino acids

Overexpression of a novel hydantoinase (hyuH) from P. aeruginosa (MCM B-887) in E. coli yielded optically pure carbamoyl amino acids. The use of optically pure carbamoyl amino acids as substrates facilitates the synthesis of non-proteinogenic amino acids. The enzyme hyuH shared a maximum of 92 % homology with proven hydantoinase protein sequences from the GenBank database, highlighting its novelty. Expression of hydantoinase gene was improved by >150 % by overexpressing it as a fusion protein in specialized E. coli CODON + host cells, providing adequate machinery for effective translation of the GC-rich gene. The presence of distinct residues in the substrate binding and active site of MCM B-887 hydantoinase enzyme explained its unique and broad substrate profile desirable for industrial applications. The purified enzyme, with a specific activity of 53U/mg of protein, was optimally active at 42 °C and pH 9.0 with a requirement of 2 mM Mn2+ ions. Supplementation of 500 mM of Na-glutamate enhanced the thermostability of the enzyme by more than 200 %.

Review on Asymmetric Transformations with Chiral Phase-Transfer Catalysts

This review focuses onasymmetric transformations with Chiral Phase-Transfer Catalysts and its application. Phase-transfer catalysis is practical methodology for organic synthesis. It is possible to achieve highly enantio selective transformations under phase-transfer conditions for a variety of ─C─C─ ─C─O─ and ─C─N─ bond-forming reactions. The asymmetric transformations using modified cinchona alkaloids, chiral spiro ammonium salts and crown ether are among the primary source of effective chiral phase-transfer catalyst, which allows access to enantiomerically pure unnatural amino acids and synthetically useful adducts containing quaternary stereogenic centers. The advantage of this method is its simple experimental procedure, large chiral pool, mild reaction condition, inexpensive, environmentally benign reagent and use of simple and inexpensive reactants. Nowadays, it appears to be the most important synthetic method used in various fields of organic chemistry, and also found widespread industrial applications. This review summarizes the synthesis application, enantio selective transformation of some selected reaction, biological activities and catalytic activities of Phase-transfer catalysis and especial emphasis is given for organo catalysis. In asymmetric organo catalyst, it is possible to obtain chiral organic products in high enantio enriched form by steric hindrance approach method. The advantage of organic molecules as chiral catalysts complements the traditional organo-metallic and biological approaches to asymmetric catalysis.

Bioactive peptides attenuate cardiac hypertrophy and fibrosis in spontaneously hypertensive rat hearts

Alcalase potato protein hydrolysate (APPH), a nutraceutical food, might an have important role in anti-obesity activity. Recent studies from our lab indicated that APPH treatment had lipolysis stimulating activity and identified was an efficient anti-obesity diet ingredient. In this study we aim to investigate the beneficial effects of pure peptide amino acid sequences (DIKTNKPVIF (DI) and IF) from APPH supplement in the regulation of cardiac hypertrophy and fibrosis on spontaneously hypertensive rats (SHR). We examined hematoxylin and eosin staining, Masson's trichrome staining, echocardiographic parameters, serum parameters, hypertrophy, inflammation and fibrotic marker expression to demonstrate efficacy of bioactive peptides in a SHR model. There was a significant upregulation between SHR and bioactive peptides treated groups in left heart weight (LHW), LHW/WHW, LHW/Tibia, LVIDd, and LVd mass. In addition, the bioactive peptides repress the protein expression of hypertrophy markers (BNP, MYH7), inflammation (TLR-4, p-NFkB, TNF-α, IL-6), and fibrotic markers (uPA, MMP-2, TIMP1, CTGF). In summary, these results indicate that DI and IF bioactive peptides from APPH attenuate cardiac hypertrophy, inflammation and fibrosis in the SHR model.

Development of Hamari Ligands for Practical Asymmetric Synthesis of Tailor-Made Amino Acids.

Enantiomerically pure tailor-made amino acids are in extremely high demand in nearly every sector of the health-related industries. In particular, the rapidly growing number of amino-acid-based pharmaceuticals calls for the development of advanced synthetic approaches featuring practicality and commercial viability. Here we provide a brief summary of the development of axially chiral tridentate Hamari ligands and their application for general asymmetric synthesis of various structural types of amino acids. The methodological diversity includes: dynamic kinetic resolution and (S)-/(R)-interconversion of unprotected amino acids and homologation of nucleophilic glycine equivalents via alkyl halide alkylation reactions as well as multiple-step transformations allowing preparation of polyfunctional and cyclic derivatives. The practicality of these methods is critically discussed.