Continuous Synthesis of Cinnarizine Salt with Malic Acid by Applying Green Chemistry Using Water-Assisted Twin Screw Extrusion.

Organic solvent-free process or green chemistry is needed for manufacturing pharmaceutical salts to avoid various environmental, safety, and manufacturing cost issues involved. In this study, a cinnarizine (CNZ) salt with malic acid at a 1:1 molar ratio was successfully prepared by twin screw extrusion (TSE) with water assistance. The feasibility of salt formation was first evaluated by screening several carboxylic acids by neat grinding (NG) and liquid-assisted grinding (LAG) using a mortar and pestle, which indicated that malic acid and succinic acid could form salts with CNZ. Further studies on salt formation were conducted using malic acid. The examination by hot-stage microscopy revealed that the addition of water could facilitate the formation and crystallization of CNZ-malic acid salt even though CNZ is poorly water-soluble. The feasibility of salt formation was confirmed by determining the pH-solubility relationship between CNZ and malic acid, where a pHmax of 2.7 and a salt solubility of 2.47 mg/mL were observed. Authentic salt crystals were prepared by solution crystallization from organic solvents for examining crystal properties and structure by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, solid-state 13C and 15N nuclear magnetic resonance (NMR), and single-crystal X-ray diffraction (SXD). These techniques also established that a salt, and not a cocrystal, was indeed formed. The CNZ salt crystals were then prepared by TSE of a 1:1 CNZ-malic acid mixture, where the addition of small amounts of water resulted in a complete conversion of the mixture into the salt form. The salts prepared by solvent crystallization and water-assisted TSE had identical properties, and their moisture sorption profiles were also similar, indicating that TSE is a viable method for salt preparation by green chemistry. Since TSE can be conducted in a continuous manner, the results of the present investigation, if combined with other continuous processes, suggest the possibility of continuous manufacturing of drug products from the synthesis of active pharmaceutical ingredients (APIs) to the production of final dosage forms.

An enzyme-centric approach for constructing an amperometric l-malate biosensor with a long and programmable linear range.

l-Malate is a key flavor enhancer and acidulant in the food and beverage industry, particularly winemaking. Enzyme-based amperometric biosensors offer convenience for monitoring its concentration. However, only a small number of off-the-shelf malate-oxidizing enzymes have been used in previous devices. These typically have linear ranges poorly suited for the l-malate concentrations found in fruit processing and winemaking, making it necessary to use precisely diluted samples. Here, we describe a pipeline of database-mining, gene synthesis, recombinant expression, and spectrophotometric assays to characterize previously untested enzymes for their suitability in biosensors. The pipeline yielded a bespoke biocatalyst-the Ascaris suum malic enzyme carrying mutation R181Q [AsME(R181Q)]. Our first prototype with AsME(R181Q) had an ultra-wide linear range of 50-200 mM l-malate, corresponding to concentrations found in undiluted fruit juices (including grape). Changing the dication from Mg2+ to Mn2+ increased sensitivity five-fold and adding citrate (100 mM) increased it another six-fold, albeit decreasing the linear range to 1-10 mM. To our knowledge, this is the first time an l-malate biosensor with a tuneable combination of sensitivity and linear range has been described. The sensor response was also tested in the presence of various molecules abundant in juices and wines, with ascorbate shown to be a potent interferent. Interference was mitigated by the addition of ascorbate oxidase, allowing for differential measurements on an undiluted, untreated wine sample that corresponded well with commercial l-malate testing kits. Overall, this work demonstrates the power of an enzyme-centric approach for designing electrochemical biosensors with improved operational parameters and novel functionality.

Fractionation and characterization of poly(ß-L-malic acid) produced by Aureobasidium melanogenum ipe-1.

Poly (ß-L-malic acid) (PMLA) is attracting industrial interest for its potential application in medicine and other industries, whose functions primarily depend upon its molecular size and chemical structure. Up to now, the fractionation and characterization of PMLA produced by Aureobasidium spp. were still unclear. In this study, the product from A. melanogenum ipe-1 was effectively fractionated using 300 and 50 kDa membranes. During the filtration, the mechanisms of membrane fouling were illegible since the PMLA can both reject and permeate the membrane, while the main fouling mechanism varied between standard blocking and complete blocking during the diafiltration. After fractionation, 14.0, 8.4 and 77.6 % of the PMLAs with Mws of 75,134, 21,344 and 10,056 Da were distributed in the 300 kDa retentate after diafiltrating, 50 kDa retentate after diafiltrating, and the 50 kDa permeate, respectively. The Mw/Mns of the PMLAs were 4.12, 1.92, and 1.12 in the three fractions. Based on characteristic spectra of NMR, HPLC and FTIR, the product was not usual L-malic acid monomers, but glucose-terminated PMLA. The glucose was located at the terminal hydroxyl of PMLA. These results would serve as a valuable guide for process design and practical operation in subsequent industrial application.

Solid state malic acid esterification on fungal α-amylase treated corn starch: Design of a green dual treatment.

For the first time, the current work applied fungal α-amylase treated corn starch in granular form to produce solid state malate-esterified starch (MES). The pores and channels created on the granules after the enzymatic modification could provide more possibilities for malic acid to esterify the starch, resulting in the increase of substitution degree (0.084) and reaction efficiency (86.6%) compared to NS. Based on the obtained results, the dual treatment significantly increased solubility, amylose content, and syneresis, but reduced transparency, viscosity, digestibility rate, and swelling power compared to those of NS. The occurrence of esterification onto starch chains was confirmed by FT-IR at 1720 cm-1. Other techniques including SEM, XRD, and DSC were employed to examine changes in the structure of starch granules after applying each treatment. Also, the greenness of the combined modification (score: 77) was proved by using a new methodology named Eco-Scale.

Structural Comparison of hMDH2 Complexed with Natural Substrates and Cofactors: The Importance of Phosphate Binding for Active Conformation and Catalysis.

Malate dehydrogenase (MDH), which catalyzes a reversible conversion of L-malate to oxaloacetate, plays essential roles in common metabolic processes, such as the tricarboxylic acid cycle, the oxaloacetate-malate shuttle, and the glyoxylate cycle. MDH2 has lately been recognized as a promising anticancer target; however, the structural information for the human homologue with natural ligands is very limited. In this study, various complex structures of hMDH2, with its substrates and/or cofactors, were solved by X-ray crystallography, which could offer knowledge about the molecular and enzymatic mechanism of this enzyme and be utilized to design novel inhibitors. The structural comparison suggests that phosphate binds to the substrate binding site and brings the conformational change of the active loop to a closed state, which can secure the substate and cofactor to facilitate enzymatic activity.

Behaviors of Organic Ligands and Phosphate during Biochar-Driven Nitrate Adsorption in the Presence of Low-Molecular-Weight Organic Acids.

A batch experiment was conducted to examine the behavior of nitrate, organic ligands, and phosphate in the co-presence of biochar and three common low-molecular-weight organic acids (LMWOAs). The results show that citrate, oxalate, and malate ions competed with nitrate ion for the available adsorption sites on the biochar surfaces. The removal rate of LMWOA ligands by the biochar via adsorption grew with increasing solution pH. The adsorbed divalent organic ligands created negatively charged sites to allow binding of cationic metal nitrate complexes. A higher degree of biochar surface protonation does not necessarily enhance nitrate adsorption. More acidic conditions formed under a higher dose of LMWOAs tended to make organic ligands predominantly in monovalent forms and failed to create negatively charged sites to bind cationic metal nitrate complexes. This could adversely affect nitrate removal efficiency in the investigated systems. LMWOAs caused significant release of phosphate from the biochar. The phosphate in the malic acid treatment tended to decrease over time, while the opposite was observed in the citric- and oxalic-acid treatments. This was caused by re-immobilization of phosphate in the former due to the marked increase in solution pH over time.

Deuterium MRSI of tumor cell death in vivo following oral delivery of 2 H-labeled fumarate.

PURPOSE: There is an unmet clinical need for direct and sensitive methods to detect cell death in vivo, especially with regard to monitoring tumor treatment response. We have shown previously that tumor cell death can be detected in vivo from 2 H MRS and MRSI measurements of increased [2,3-2 H2 ]malate production following intravenous injection of [2,3-2 H2 ]fumarate. We show here that cell death can be detected with similar sensitivity following oral administration of the 2 H-labeled fumarate. METHODS: Mice with subcutaneously implanted EL4 tumors were fasted for 1 h before administration (200 µl) of [2,3-2 H2 ]fumarate (2 g/kg bodyweight) via oral gavage without anesthesia. The animals were then anesthetized, and after 30 min, tumor conversion of [2,3-2 H2 ]fumarate to [2,3-2 H2 ]malate was assessed from a series of 13 2 H spectra acquired over a period of 65 min. The 2 H spectra and 2 H spectroscopic images were acquired using a surface coil before and at 48 h after treatment with a chemotherapeutic drug (etoposide, 67 mg/kg). RESULTS: The malate/fumarate signal ratio increased from 0.022 ± 0.03 before drug treatment to 0.12 ± 0.04 following treatment (p = 0.023, n = 4). Labeled malate was undetectable in spectroscopic images acquired before treatment and increased in the tumor area following treatment. The increase in the malate/fumarate signal ratio was similar to that observed previously following intravenous administration of labeled fumarate. CONCLUSION: Orally administered [2,3-2 H2 ]fumarate can be used to detect tumor cell death noninvasively following treatment with a sensitivity that is similar to that obtained with intravenous administration.

Serine acetyltransferase from Neisseria gonorrhoeae; structural and biochemical basis of inhibition.

Serine acetyltransferase (SAT) catalyzes the first step in the two-step pathway to synthesize l-cysteine in bacteria and plants. SAT synthesizes O-acetylserine from substrates l-serine and acetyl coenzyme A and is a key enzyme for regulating cellular cysteine levels by feedback inhibition of l-cysteine, and its involvement in the cysteine synthase complex. We have performed extensive structural and kinetic characterization of the SAT enzyme from the antibiotic-resistant pathogen Neisseria gonorrhoeae. Using X-ray crystallography, we have solved the structures of NgSAT with the non-natural ligand, l-malate (present in the crystallization screen) to 2.01 Šand with the natural substrate l-serine (2.80 Å) bound. Both structures are hexamers, with each monomer displaying the characteristic left-handed parallel ß-helix domain of the acyltransferase superfamily of enzymes. Each structure displays both extended and closed conformations of the C-terminal tail. l-malate bound in the active site results in an interesting mix of open and closed active site conformations, exhibiting a structural change mimicking the conformation of cysteine (inhibitor) bound structures from other organisms. Kinetic characterization shows competitive inhibition of l-cysteine with substrates l-serine and acetyl coenzyme A. The SAT reaction represents a key point for the regulation of cysteine biosynthesis and controlling cellular sulfur due to feedback inhibition by l-cysteine and formation of the cysteine synthase complex. Data presented here provide the structural and mechanistic basis for inhibitor design and given this enzyme is not present in humans could be explored to combat the rise of extensively antimicrobial resistant N. gonorrhoeae.

Improved Synthesis of a Novel Biodegradable Tunable Micellar Polymer Based on Partially Hydrogenated Poly(ß-malic Acid-co-benzyl Malate).

Poly(benzyl malate) (PBM), together with its derivatives, have been studied as nanocarriers for biomedical applications due to their superior biocompatibility and biodegradability. The acquisition of PBM is primarily from chemical routes, which could offer polymer-controlled molecular weight and a unique controllable morphology. Nowadays, the frequently used synthesis from L-aspartic acid gives an overall yield of 4.5%. In this work, a novel synthesis route with malic acid as the initiator was successfully designed and optimized, increasing the reaction yield up to 31.2%. Furthermore, a crystalline form of PBM (PBM-2) that polymerized from high optical purity benzyl-ß-malolactonate (MLABn) was discovered during the optimization process. X-ray diffraction (XRD) patterns revealed that the crystalline PBM-2 had obvious diffraction peaks, demonstrating that its internal atoms were arranged in a more orderly manner and were different from the amorphous PBM-1 prepared from the racemic MLABn. The differential scanning calorimetry (DSC) curves and thermogravimetric curves elucidated the diverse thermal behaviors between PBM-1 and PBM-2. The degradation curves and scanning electron microscopy (SEM) images further demonstrated the biodegradability of PBM, which have different crystal structures. The hardness of PBM-2 implied the potential application in bone regeneration, while it resulted in the reduction of solubility when compared with PBM-1, which made it difficult to be dissolved and hydrogenated. The solution was therefore heated up to 75 °C to achieve benzyl deprotection, and a series of partially hydrogenated PBM was sequent prepared. Their optimal hydrogenation rates were screened to determine the optimal conditions for the formation of micelles suitable for drug-carrier applications. In summary, the synthesis route from malic acid facilitated the production of PBM for a shorter time and with a higher yield. The biodegradability, biosafety, mechanical properties, and adjustable hydrogenation widen the application of PBM with tunable properties as drug carriers.

Nanoprecipitation of Biocompatible Poly(malic acid) Derivative, Its Ability to Encapsulate a Molecular Photothermal Agent and Photothermal Properties of the Resulting Nanoparticles.

Biocompatible nanoparticles (NPs) of hydrophobic poly(benzyl malate) (PMLABe) were prepared by nanoprecipitation. The influence of nanoprecipitation parameters (initial PMLABe, addition rate, organic solvent/water ratio and stirring speed) were studied to optimize the resulting formulations in terms of hydrodynamic diameter (Dh) and dispersity (PDI). PMLABe NPs with a Dh of 160 nm and a PDI of 0.11 were isolated using the optimized nanoprecipitation conditions. A hydrophobic near infra-red (NIR) photothermally active nickel-bis(dithiolene) complex (Ni8C12) was then encapsulated into PMLABe NPs using the optimized nanoprecipitation conditions. The size and encapsulation efficiency of the NPs were measured, revealing that up to 50 weight percent (wt%) of Ni8C12 complex can efficiently be encapsulated with a slight increase in Dh of the corresponding Ni8C12-loaded NPs. Moreover, we have shown that NP encapsulating Ni8C12 were stable under storage conditions (4 °C) for at least 10 days. Finally, the photothermal properties of Ni8C12-loaded NPs were evaluated and a high photothermal efficiency (62.7 ± 6.0%) waswas measured with NPs incorporating 10 wt% of the Ni8C12 complex.

Evaluation of easy-removing antioxidant films of chitosan with Melaleuca alternifolia essential oil.

Chitosan - tea tree essential oil (TTEO) films were obtained as a new biodegradable material. Malic acid or lactic acid solvents were evaluated to obtain easy-removing films. The microstructure by SEM and FT-IR, the thermal properties by TGA/DSC, the mechanical properties, the water vapor permeability, the antioxidant (DPPH• and ABTS•+) activity and the optical properties of the formulated films were evaluated. A complete dissolution of the film in water was obtained. The elongation to break was higher in the films with malic acid (145.88-317.33%), comparing with those with lactic acid (25.54-44.08%). Chitosan film obtained in malic acid with TTEO showed the highest antioxidant activity. The colour and transparency of the samples did not suffer significant variations by TTEO addition. Films showed good UV-barrier properties, with a slightly improvement by TTEO addition. The films obtained showed a great potential for food packaging applications.

Whey permeate as a substrate for the production of freeze-dried Lactiplantibacillus plantarum to be used as a malolactic starter culture.

The aim of this work was to obtain freeze-dried biomass of the native Patagonian Lactiplantibacillus plantarum strain UNQLp 11 from a whey permeate (WP)-based medium and compare it with the growth in commercial MRS broth medium. Survival and activity of the freeze-dried Lb. plantarum strain were investigated after inoculation in wine as a starter culture for malolactic fermentation (MLF). The effect of storage and rehydration condition of the dried bacteria and the nutrient supplementation of wine were also studied. The freeze-dried cultures from WP and those grown in MRS showed similar survival results. Rehydration in MRS broth for 24 h and the addition of a rehydration medium to wine as nutrient supplementation improved the survival under wine harsh conditions and guaranteed the success of MLF. Storage at 4 °C under vacuum was the best option, maintaining high cell viability for at least 56 days, with malic acid consumption higher than 90% after 7 days of inoculation in a wine-like medium. These results represent a significant advance for sustainable production of dried malolactic starter cultures in an environmentally friendly process, which is low cost and easy to apply in winemaking under harsh physicochemical conditions.

New Crystalline Salts of Nicotinamide Riboside as Food Additives.

NR+ is a highly effective vitamin B3 type supplement due to its unique ability to replenish NAD+ levels. While NR+ chloride is already on the market as a nutritional supplement, its synthesis is challenging, expensive, and low yielding, making it cumbersome for large-scale industrial production. Here we report the novel crystalline NR+ salts, d/l/dl-hydrogen tartrate and d/l/dl-hydrogen malate. Their high-yielding, one-pot manufacture does not require specific equipment and is suitable for multi-ton scale production. These new NR+ salts seem ideal for nutritional applications due to their bio-equivalence compared to the approved NR+ chloride. In addition, the crystal structures of all stereoisomers of NR+ hydrogen tartrate and NR+ hydrogen malate and a comparison to the known NR+ halogenides are presented.

The efficiency and mechanism of a new absorption enhancer, malic acid, for enhancing the oral bioavailability of docetaxel.

This study investigated the efficiency and the related mechanisms of a new absorption enhancer, DL-malic acid (MA), on the oral bioavailability of docetaxel (DTX). Polyethylene glycol polycarbonate (PEG-PCL) modified liposomes (PLip) were prepared for DTX, and incorporated into the pH-sensitive microspheres (MS) with sustained release. MA decreased the transepithelial electrical resistance (TEER) across a Caco-2 cell monolayer by 20% and 57% after 2 and 3 h of co-incubation with DTX-PLip and the cells, respectively, indicating that MA could open tight junctions but not instantaneously. After long enough exposure (4 h) of MA to the small intestine of rats, only the absorption rate constant (ka) of DTX-PLip, but not Duopafei®, was increased, which could be related to the intestinal mucosal permeability of DTX. After co-administration in rats, MA significantly enhanced the oral bioavailability of DTX in DTX-PLip-MS from 44.67% to 81.27%, rather than DTX-PLip and Duopafei®, which could be related to the prolonged intestinal retention time of DTX-PLip via the MS and the promoted drug intercellular transport by MA. The absorption-enhancing effects of MA on DTX-PLip-MS were further confirmed by in vivo imaging. The above findings suggest that MA served as a new and efficient absorption enhancer for DTX-PLip-MS.HIGHlIGHTSIn this study, malic acid as a new absorption enhancer for DTX in polymer-liposome (PLip) embedded in pH-sensitive microspheres (MS) was found for the first time.The malic acid could significantly enhance oral bioavailability of DTX in DTX-PLip-MS (from 44.67 % to 81.27%) rather than Duopafei® and DTX-PLip after co-administration.The absorption enhancement may be closely related to the intestinal retention time and mucosal permeability.These findings will provide an important reference for the study of absorption enhancers for promoting intercellular insoluble drug transport.

Structural basis for the interaction modes of dihydroorotase with the anticancer drugs 5-fluorouracil and 5-aminouracil.

Dihydroorotase (DHOase) is the third enzyme in the de novo biosynthesis pathway of pyrimidine nucleotides and considered an attractive target for potential antimalarial, anticancer, and antipathogen chemotherapy. Whether the FDA-approved clinical drug 5-fluorouracil (5-FU) that is used to target the enzyme thymidylate synthase for anticancer therapy can also bind to DHOase remains unknown. Here, we report the crystal structures of DHOase from Saccharomyces cerevisiae (ScDHOase) complexed with malate, 5-FU, and 5-aminouracil (5-AU). ScDHOase shares structural similarity with Escherichia coli DHOase. We also characterized the binding of 5-FU and 5-AU to ScDHOase by using the fluorescence quenching method. These complexed structures revealed that residues Arg18, Asn43, Thr106, and Ala275 of ScDHOase were involved in the 5-FU (PDB entry 6L0B) and 5-AU binding (PDB entry 6L0F). Overall, these results provide structural insights that may facilitate the development of new inhibitors targeting DHOase and constitute the 5-FU and 5-AU interactomes for further clinical chemotherapies.

Structure and inhibition mechanism of the human citrate transporter NaCT.

Citrate is best known as an intermediate in the tricarboxylic acid cycle of the cell. In addition to this essential role in energy metabolism, the tricarboxylate anion also acts as both a precursor and a regulator of fatty acid synthesis1-3. Thus, the rate of fatty acid synthesis correlates directly with the cytosolic concentration of citrate4,5. Liver cells import citrate through the sodium-dependent citrate transporter NaCT (encoded by SLC13A5) and, as a consequence, this protein is a potential target for anti-obesity drugs. Here, to understand the structural basis of its inhibition mechanism, we determined cryo-electron microscopy structures of human NaCT in complexes with citrate or a small-molecule inhibitor. These structures reveal how the inhibitor-which binds to the same site as citrate-arrests the transport cycle of NaCT. The NaCT-inhibitor structure also explains why the compound selectively inhibits NaCT over two homologous human dicarboxylate transporters, and suggests ways to further improve the affinity and selectivity. Finally, the NaCT structures provide a framework for understanding how various mutations abolish the transport activity of NaCT in the brain and thereby cause epilepsy associated with mutations in SLC13A5 in newborns (which is known as SLC13A5-epilepsy)6-8.

Impact of esterification with malic acid on the structural characteristics and in vitro digestibilities of different starches.

This research focused on the structural characteristics of resistant starches (RSs) that were obtained from corn, potato, and sweet potato and esterified by L-malic acid. Further, the unique effect of the degree of substitution (DS) on the crystalline properties was studied. Different starches were allowed to react with 2 M malic acid (pH 1.5) for 12 h at 130 °C. The shapes of the granules and the Maltese-cross shapes of samples were maintained and visible under an optical microscope. The FT-IR spectrum displayed evident carbonyl peaks at 1740 cm-1, and the onset temperature (To) and gelatinization enthalpy (∆H) gradually decreased as DS increased. The malic acid-treated starches exhibited an increased RS content compared to those of the control. The RS contents of potato, sweet potato, and corn, which were 65.5%, 70.0%, and 89.8% in the uncooked MT-samples, decreased to 57.3%, 63.8%, and 86.7% in the cooked MT-samples, respectively, and exhibited high heat stability; corn starch yielded the highest RS among them. The thermal and malic acid treatments resulted in the partial hydrolysis and rearrangement of the helix structure of crystalline area, which was affected by esterification. The result revealed that the RS content increased as that of DS escalated.

Salt Engineering of Aripiprazole with Polycarboxylic Acids to Improve Physicochemical Properties.

Aripiprazole (APZ) has poor physicochemical properties and bitter taste. The current study aimed to prepare salts of APZ with polycarboxylic acids (citric, malic, and tartaric acids) to improve physicochemical properties and impart sour taste to the drug. The salts were prepared by solubilization-crystallization method, and characterized by electron microscopic, spectroscopic, diffractometry, and thermal methods. The salts were assessed for pH solubility, pH-stability, dissolution, and solid-state stability. Fourier transformed infrared, X-ray powder diffraction, and differential scanning calorimetry data indicated formation of new solid phases. APZ and the salts exhibited pH-dependent solubility. The pH solubility curve shape was inverted "V," inverted "W," and inverted "U" for APZ, APZ-Citrate, and APZ-Malate and APZ-Tartrate, respectively. Compared to APZ, the solubility of salts at pH 4, 5, and 6 was 3.6-7.1, 23.9-31.5, and 143.4-373.3 folds of APZ. Increase in solubility in water by citrate, malate, and tartrate salts was 5562.8, 21,284.7, and 22,846.7 folds of APZ. The salt formation also leads to an increase in rate and extent of dissolution. The dissolution extent was 3.5 ± 0.5, 71.3 ± 1.2, 80.1 ± 6.2, and 86.1 ± 1.1% for APZ, APZ-Citrate, APZ-Malate, and APZ-Tartrate, respectively. Liquid and solid-state stabilities of the salts were comparable to APZ. In conclusion, salts of APZ with polycarboxylic acids improved solubility, and dissolution, and impart sour taste, which may improve palatability of the drug.

Speciation of essential nutrient trace elements in coconut water.

Coconut water (Cocos Nucifera) is shown to be a source of essential elements present in the form of low-molecular weight stable complexes known for their bio-availability. The total element concentrations were in the range of 0.2-2.7, 0.3-1, 3-14 and 0.5-2 ppm for Fe, Cu, Mn, and Zn, respectively, and varied as a function of the origin of the nut and its maturity. Speciation was investigated by size-exclusion chromatography - inductively coupled plasma mass spectrometry (ICPMS), and hydrophilic interaction liquid chromatography (HILIC) - electrospray-OrbitrapMS. The metal species identified included: iron complexes with citrate and malate: FeIII(Cit)3(Mal), FeIII(Cit)2(Mal)2, FeIII(Mal)2, glutamine: FeIII(Glu)2 and nicotianamine: FeII(NA); copper complexes with phenylanine: CuII(Phe)2 and CuII(Phe)3 and nicotianamine: CuII(NA); zinc complexes with citrate: ZnII(Cit)2 and nicotianamine ZnII(NA) and manganese complex with asparagine MnII(Asp)2. The contributions of the individual species to the total elements concentrations could be estimated by HILIC - ICP MS.

A Unified Approach to Phytosiderophore Natural Products.

This work reports on the concise total synthesis of eight natural products of the mugineic acid and avenic acid families (phytosiderophores). An innovative "east-to-west" assembly of the trimeric products resulted in a high degree of divergence enabling the formation of the final products in just 10 or 11 steps each with a minimum of overall synthetic effort. Chiral pool starting materials (l-malic acid, threonines) were employed for the outer building blocks while the middle building blocks were accessed by diastereo- and enantioselective methods. A highlight of this work consists in the straightforward preparation of epimeric hydroxyazetidine amino acids, useful building blocks on their own, enabling the first synthesis of 3''-hydroxymugineic acid and 3''-hydroxy-2'-deoxymugineic acid.