Synthesis Of Hydroxamates Research Articles

Cofactor Complexes of DesD, a Model Enzyme in the Virulence-related NIS Synthetase Family.

The understudied nonribosomal-peptide-synthetase-independent siderophore (NIS) synthetase family has been increasingly associated with virulence in bacterial species due to its key role in the synthesis of hydroxamate and carboxylate "stealth" siderophores. We have identified a model family member, DesD, from Streptomyces coelicolor, to structurally characterize using a combination of a wild-type and a Arg306Gln variant in apo, cofactor product AMP-bound, and cofactor reactant ATP-bound complexes. The kinetics in the family has been limited by solubility and reporter assays, so we have developed a label-free kinetics assay utilizing a single-injection isothermal-titration-calorimetry-based method. We report second-order rate constants that are 50 times higher than the previous estimations for DesD. Our Arg306Gln DesD variant was also tested under identical buffer and substrate conditions, and its undetectable activity was confirmed. These are the first reported structures for DesD, and they describe the critical cofactor coordination. This is also the first label-free assay to unambiguously determine the kinetics for an NIS synthetase.

Synthesis of Hydroxamic Acid Derivatives Using Blocked (Masked) O-Isocyanate Precursors.

Hydroxamic acids are present in a several pharmaceuticals and agrochemicals. Synthetic strategies providing access to hydroxamic acid derivatives remain limited, typically requiring the use of nucleophilic hydroxylamine reagents. Herein, a synthesis of hydroxamates from unactivated carboxylic acids is reported making use of rare blocked (masked) O-substituted isocyanates. The applicability of this transformation was highlighted by targeting the synthesis of vorinostat and belinostat derivatives.

Substrate‐Bound Complex of DesD, a Model Enzyme in the Virulence‐Related NIS Synthetase Family

The understudied NIS Synthetase family have been increasingly associated with virulence in bacterial species, due to their key role in the synthesis of hydroxamate and carboxylate “stealth” siderophores. We have identified a model family member, DesD from Streptomyces coelicolor, to characterize structurally using a combination of wild‐type and Arg306Gln variant in apo, cofactor product (AMP)‐bound with analog cadaverine, and cofactor bound with analog dfoB complexes. Kinetics in the family have been limited by solubility and reporter‐based assays, so we have developed a label‐free kinetics assay utilizing an unusual single‐injection isothermal titration calorimetry based method. We report second order rate constants 50‐fold higher than the previous estimations for DesD in both the cofactor‐limiting and dfoG substrate limiting curves. Our Arg306Gln DesD variant was also tested in identical buffer and substrate conditions, and confirmed undetectable activity. This is the first complete complex structure (cofactor, amine and carboxylate) reported for an NIS synthetase, and the first label‐free assay to unambiguously determine kinetics for the NIS synthetase family. Our future directions aim to quantify binding thermodynamics, characterize the small substrates (two molecules of hydroxysuccinylcadaverine, which must be synthesized) and delineate the active site mechanism with site‐directed mutagenesis.Support or Funding InformationThis research was supported in part by the National Science Foundation (NSF‐RUI grant 1716986 to K.M.H.), by the John Stauffer Charitable Trust.The DesD dimer has two active sites, only one of which is filled with substrate in the structures (left). The small substrate analog cadaverine (yellow atom coloring) is shown bound to wild‐type DesD at the bottom right, and the large substrate dfoB (magenta atom coloring) is bound to Arg306Gln in the top right. Both structures are shown with cofactor ATP (teal atom coloring) bound as well.Figure 1

Hiết kế, tổng hợp và đánh giá khả năng ức chế enzyme histone deacetylase (HDAC) in silico của một số dẫn xuất tương tự belinostat

Belinostat is a histone deacetylase inhibitor for the treatment of hematological malignancies and solid tumor. In this study, belinostat analogues were successfully synthesized through a simple and effective process suited to laboratory scale in Vietnam including 6 steps: i) Preparation of m-nitrobenzaldehyde using KNO3/H2SO4; ii) Use of Wittig reaction with ylide compound as the nucleophile; iii) Reduction of –NO2 group. iv) Preparation of sulfonyl; v) Substitution reaction with amines as the nucleophile; and vi) Synthesis of hydroxamate by NH2OH. Belinostat derivatives were obtained in good yields. The structures of the products were confirmed by 1H-NMR and MS spectra. The evaluation of HDAC inhibitory capacity of the synthesized compounds in silico was also carried out to investigate the biological activity.

Bioprocess development for nicotinic acid hydroxamate synthesis by acyltransferase activity of Bacillus smithii strain IITR6b2

In this work, acyltransferase activity of a new bacterial isolate Bacillus smithii strain IITR6b2 was utilized for the synthesis of nicotinic acid hydroxamate (NAH), a heterocyclic class of hydroxamic acid. NAH is an important pyridine derivative and has found its role as bioligand, urease inhibitor, antityrosinase, antioxidant, antimetastatic, and vasodilating agents. Amidase having acyltransferase activity with nicotinamide is suitable for nicotinic acid hydroxamate production. However, amidase can also simultaneously hydrolyze nicotinamide and nicotinic acid hydroxamate to nicotinic acid. Nicotinic acid is an undesirable by-product and thus any biocatalytic process involving amidase for nicotinic acid hydroxamate production needs to have high ratios of acyltransferase to amide hydrolase and acyltransferase to nicotinic acid hydroxamate hydrolase activity. Isolate Bacillus smithii strain IITR6b2 was found to have 28- and 12.3-fold higher acyltransferase to amide and hydroxamic acid hydrolase activities, respectively. This higher ratio resulted in a limited undesirable by-product, nicotinic acid (NA) synthesis. The optimal substrate/co-substrate ratio, pH, temperature, incubation time, and resting cells concentration were 200/250 mM, 7, 30 °C, 40 min, and 0.7 mg(DCW) ml(-1), respectively, and 94.5 % molar conversion of nicotinamide to nicotinic acid hydroxamate was achieved under these reaction conditions. To avoid substrate inhibition effect, a fed-batch process based on the optimized parameters with two feedings of substrates (200/200 mM) at 40-min intervals was developed and a molar conversion yield of 89.4 % with the productivity of 52.9 g h(-1) g (DCW) (-1) was achieved at laboratory scale. Finally, 6.4 g of powder containing 58.5 % (w/w) nicotinic acid hydroxamate was recovered after lyophilization and further purification resulted in 95 % pure product.

A NovelL-Amino Acid Ligase fromBacillus subtilisNBRC3134, a Microorganism Producing Peptide-Antibiotic Rhizocticin

L-amino acid ligase catalyzes the formation of an alpha-peptide bond from unprotected L-amino acids in an ATP-dependent manner, and this enzyme is very useful in efficient peptide production. We performed enzyme purification to obtain a novel L-amino acid ligase from Bacillus subtilis NBRC3134, a microorganism producing peptide-antibiotic rhizocticin. Rhizocticins are dipeptide or tripeptide antibiotics and commonly possess L-arginyl-L-2-amino-5-phosphono-3-cis-pentenoic acid. The purification was carried out by detecting L-arginine hydroxamate synthesis activity, and a target enzyme was finally purified 1,280-fold with 0.8% yield. The corresponding gene was then cloned and designated rizA. rizA was 1,242 bp and coded for 413 amino acid residues. Recombinant RizA was prepared, and it was found that the recombinant RizA synthesized dipeptides whose N-terminus was L-arginine in an ATP-dependent manner. RizA had strict substrate specificity toward L-arginine as the N-terminal substrate; on the other hand, the substrate specificity at the C-terminus was relaxed.

Solid-Phase Synthesis of Biologically Interesting Compounds Containing Hydroxamic Acid Moiety

Chemical strategies developed for the solid-phase synthesis of hydroxamates are divided into four groups: (i) the traditional synthesis of hydroxamates via cleavage of resin-bound esters by hydroxylamine and its derivatives, (ii) introduction of hydroxamic acid moiety on the resin-bound precursor, (iii) transformation of polymer-supported hydroxylamine, attached to a solid supported linker either by oxygen (O-linking strategy) or by nitrogen (N-linking strategy), and (iv) synthesis of N-alkyl hydroxamates. The scope and limitation of individual approaches are discussed.

ChemInform Abstract: Direct Synthesis of Hydroxamates from Carboxylic Acids Using 2‐Mercaptopyridone‐1‐oxide‐based Thiouronium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Direct synthesis of hydroxamates from carboxylic acids using 2-mercaptopyridone-1-oxide-based thiouronium salts

Tetrafluoroborate and hexafluorophosphate thiouronium salts derived from 2-mercaptopyridone-1-oxide and tetramethylurea (TOTT and HOTT) or N,N′-dimethylpropyleneurea (TODT and HODT) convert carboxylic acids to Weinreb amides and N-methoxy or N-benzoxyamides in high yields by reaction with N,O-dimethylhydroxylamine and O-methyl- or O-benzyl-hydroxylamine hydrochlorides, respectively, in the presence of triethylamine or DIEA.

Growth and siderophore production inBradyrhizobium (lupin) strains under iron limitation

SixBradyrhizobium (lupin) strains were evaluated for their ability to produce siderophores using four chemical assays. Two strains gave positive reactions with chrome azurol S assay (CAS) and produced hydroxamate-type siderophores. The other four strains gave negative results for siderophore production using the four assays. Generation time, growth yield and hydroxamate production of one strain (WPBS 3201 D) were affected by the iron concentration of the culture medium and the previous culture history of the cells. Resuspension of washed cells grown previously in media supplemented with 0 and 20 μmol/L Fe into differing iron regimes (0, 0.5, 1, 2, 4, 8, 10, 15 and 20 μmol/L Fe) suggest that the extent of hydroxamate production depended on the growth history of the cells. Cells pregrown in 20 μmol/L Fe produced a high amount of hydroxamates compared with cells pregrown in iron-free medium when resuspended in medium containing up to 4 μmol/L Fe. Cells pregrown in 20 μmol/L Fe were more sensitive to iron repression than those pregrown in 0.5 μmol/L Fe. Mannitol was the best carbon source for siderophore production. Siderophore synthesis was inhibited by 4-chloromercuribenzenesulfonic acid, 2,4-dinitrophenol, sodium azide and MgCl2 suggesting that an energized membrane and a mercapto group are essential and required for hydroxamate synthesis in strain WPB5 3201 D.

Growth and siderophore production in vitro of Bradyrhizobium (Lupin) strains under iron limitation

Six Bradyrhizobium (lupin) strains were evaluated for their ability to produce in vitro siderophores using four chemical assays. Bradyrhizobium strains WPBS 3201 D and 3211 D gave positive reactions with the chrome azurol S assay (CAS) and produced hydroxamate-type siderophores. The other four strains (USDA 3040, 3041, 3042 and CB 2272) gave negative results for siderophore production with the four assays. The generation time, growth yield and hydroxamate production of strain WPBS 3201 D were affected by the iron concentration of the culture medium and the previous culture history of the cells. Resuspension of washed cells grown previously in media supplemented with 0 and 20 μmol·L −1 Fe into differing iron regimes (0 and 20 μmol·L −1 Fe) suggest that the extent of hydroxamate production was dependent on the growth history of the cells. Cells pre-grown in 20 μmol·L Fe produced a high amount of hydroxamates compared with cells pre-grown in iron-free medium when resuspended in medium containing up 4 μmol·L −1 Fe. Cells pre-grown in 20 μmol·L −1 Fe were also more sensitive to iron repression than those pre-grown in 0.5 μmol·L Fe. Mannitol was the best carbon source for siderophore production. Siderophore synthesis was inhibited by 4-chloromercuribenzenesulfonic acid, 2,4-dinitrophenol, sodium azide and MgCl 2 suggesting that an energized membrane and a mercapto group are essential and required for hydroxamate synthesis in Bradyrhizobium (lupin) strain WPBS 3201 D.

Hydroxamic acids as potent inhibitors of endothelin-converting enzyme from human bronchiolar smooth muscle.

Hydroxamic acids 6a-h, derived from malonyl amino acids, and 25a-d, derived from succinyl amino acids, were synthesized as inhibitors of human bronchiolar smooth muscle endothelin-converting enzyme (HBSM ECE). Several unexpected side reactions were discovered, particularly in the synthesis of hydroxamates derived from succinates. In vitro evaluation against human bronchiolar ECE revealed that in all cases hydroxamates derived from malonate were more potent than hydroxamates derived from succinate. Isopropyl and isobutyl P1' side chains were suitable; omission of the P1' side chain seriously diminished potency. In the P2' position, several amino acids gave potent malonate-derived hydroxamate inhibitors (6b, d-h, IC50 = 0.2-6.8 nM), and beta-Ala provided an extremely potent inhibitor (6c, IC50 = 0.01 nM). C-terminus carboxylates are much more potent ECE inhibitors than the corresponding amides. Most of the hydroxamates were also potent inhibitors of thermolysin and neutral endopeptidase (NEP); however, the P2' beta-Ala derivative 6c uniquely inhibited HBSM ECE much more potently than NEP.

Biosynthetically active glutamine synthetase in the marine diatom Phaeodactylum tricornutum: optimization of the forward-reaction assay

The activity of glutamine synthetase (GS) was measured in the marine diatom Phaeodactylum tricornutum Bohlin (Strain SME) by a biosynthetic assay, based on γ-glutamyl hydroxamate synthesis, and referred to as the forwardreaction assay. The effects of pH, temperature and different homogenizing buffer preparations on enzyme activity, linearity of reactions, and substrate-saturation kinetics were investigated. The resultant data provide the basis for establishing optimum experimental conditions for a standard assay. Affinities of P. tricornutum GS for glutamate, ATP and Mg2+ were similar to those recorded elsewhere for a variety of other phytoplankton species using “true” biosynthetic assays based on release of inorganic phosphate, whereas the affinity for hydroxylamine was two orders of magnitude lower than that for ammonium, with an apparent Km value in the millimolar range. This, together with negative results obtained during earlier attempts to detect GS activity in P. tricornutum using the “true” biosynthetic assay, indicates that the GS of this alga has a lower affinity for ammonium than that of other phytoplankton species. Dual substrate kinetics demonstrated that apparent Km and Vm values for glutamate were directly proportional to the concentration of ATP, thus giving indirect evidence of a correlation between GS activity and the adenylate energy charge. Comparisons between synthetase activities obtained with the optimized forward-reaction assay and transferase activities reported from other studies on various phytoplankton species revealed discrepancies which, to a great extent, probably arise from differences in the growth conditions of the organisms.

Hydroxamate-mediated transport of iron controlled by ColV plasmids.

A new high-affinity system for iron transport, associated with the presence of ColV plasmids, has been detected in Escherichia coli and partially characterized. The presence of such "iron-transport plasmids" in E. coli cells that are defective in enterochelin-mediated transport of iron enabled them to grow in media to which 2,2'-dipyridyl had been added to reduce availability of iron. In addition, the presence of plasmid deoxyribonucleic acid in a mutant defective in enterochelin biosynthesis was associated with a marked increase in the rate of radioactive-iron uptake. Plasmid-determined uptake of iron was distinct from previously recognized systems for iron transport in E. coli K-12, and the colicin V molecule appeared not to be directly involved. Hydroxylamine-nitrogen could be detected in cell pellets of ColV+ cultures, and similar material was detected in supernatant fluids of late log- or stationary-phase cultures. The hydroxamate material was not detected in cell pellets or culture supernatants of strains from which plasmids had been eliminated, and a 95% decrease in hydroxamate synthesis was observed when cells were grown in minimal medium containing 2 microM iron.