Synthesis and Biological Evaluation of Fluorine-18 and Deuterium Labeled l-Fluoroalanines as Positron Emission Tomography Imaging Agents for Cancer Detection.

To fully explore the potential of 18F-labeled l-fluoroalanine for imaging cancer and other chronic diseases, a simple and mild radiosynthesis method has been established to produce optically pure l-3-[18F]fluoroalanine (l-[18F]FAla), using a serine-derivatized, five-membered-ring sulfamidate as the radiofluorination precursor. A deuterated analogue, l-3-[18F]fluoroalanine-d3 (l-[18F]FAla-d3), was also prepared to improve metabolic stability. Both l-[18F]FAla and l-[18F]FAla-d3 were rapidly taken up by 9L/lacZ, MIA PaCa-2, and U87MG cells and were shown to be substrates for the alanine-serine-cysteine (ASC) amino acid transporter. The ability of l-[18F]FAla, l-[18F]FAla-d3, and the d-enantiomer, d-[18F]FAla-d3, to image tumors was evaluated in U87MG tumor-bearing mice. Despite the significant bone uptake was observed for both l-[18F]FAla and l-[18F]FAla-d3, the latter had enhanced tumor uptake compared to l-[18F]FAla, and d-[18F]FAla-d3 was not specifically taken up by the tumors. The enhanced tumor uptake of l-[18F]FAla-d3 compared with its nondeuterated counterpart, l-[18F]FAla, warranted the further biological investigation of this radiotracer as a potential cancer imaging agent.

Efficient synthetic methods for α,ß-dehydroamino acids as useful and environmentally benign building blocks in biological and materials science.

Both natural and unnatural amino acids, peptides, and proteins are widely recognized as green and sustainable organic chemicals, not only in the field of biological sciences but also in materials science. It has been discovered that artificially designed unnatural peptides and proteins exhibit advanced properties in medical and materials science. In this context, the development of precise chemical modification methods for amino acids and peptides is acknowledged as an important research project in the field of organic synthesis. While a wide variety of modification methods for amino acid residues have been developed to artificially modify peptides and proteins, the representative methods for modifying amino acid residues have traditionally relied on the nucleophilic properties of the functionalities on the residues. In this context, the development of different modification methods using an umpolung-like approach by utilizing the electrophilic nature of amino acid derivatives appears to be very attractive. One of the promising electrophilic amino acid compounds for realizing important modification methods of amino acid derivatives is α,ß-dehydroamino acids, which possess an α,ß-unsaturated carbonyl structure. This review article summarizes methods for the preparation of α,ß-dehydroamino acids derived from natural and unnatural amino acid derivatives. The utilities of α,ß-dehydroamino acid derivatives, including peptides and proteins containing dehydroalanine units, in bioconjugations are also discussed.

Design, Synthesis and Molecular Docking Study of Novel 3-Phenyl-ß-Alanine-Based Oxadiazole Analogues as Potent Carbonic Anhydrase II Inhibitors.

Carbonic anhydrase-II (CA-II) is strongly related with gastric, glaucoma, tumors, malignant brain, renal and pancreatic carcinomas and is mainly involved in the regulation of the bicarbonate concentration in the eyes. With an aim to develop novel heterocyclic hybrids as potent enzyme inhibitors, we synthesized a series of twelve novel 3-phenyl-ß-alanine 1,3,4-oxadiazole hybrids (4a-l), characterized by 1H- and 13C-NMR with the support of HRESIMS, and evaluated for their inhibitory activity against CA-II. The CA-II inhibition results clearly indicated that the 3-phenyl-ß-alanine 1,3,4-oxadiazole derivatives 4a-l exhibited selective inhibition against CA-II. All the compounds (except 4d) exhibited good to moderate CA-II inhibitory activities with IC50 value in range of 12.1 to 53.6 µM. Among all the compounds, 4a (12.1 ± 0.86 µM), 4c (13.8 ± 0.64 µM), 4b (19.1 ± 0.88 µM) and 4h (20.7 ± 1.13 µM) are the most active hybrids against carbonic CA-II. Moreover, molecular docking was performed to understand the putative binding mode of the active compounds. The docking results indicates that these compounds block the biological activity of CA-II by nicely fitting at the entrance of the active site of CA-II. These compounds specifically mediating hydrogen bonding with Thr199, Thr200, Gln92 of CA-II.

Direct and Catalytic C-Glycosylation of Arenes: Expeditious Synthesis of the Remdesivir Nucleoside.

Since early 2020, scientists have strived to find an effective solution to fight SARS-CoV-2, in particular by developing reliable vaccines that inhibit the spread of the disease and repurposing drugs for combatting its effects on the human body. The antiviral prodrug Remdesivir is still the most widely used therapeutic during the early stages of the infection. However, the current synthetic routes rely on the use of protecting groups, air-sensitive reagents, and cryogenic conditions, thus impeding a cost-efficient supply to patients. We have, therefore, focused on the development of a straightforward, direct addition of (hetero)arenes to unprotected sugars. Here we report a silylium-catalyzed and completely stereoselective C-glycosylation that initially yields the open-chain polyols, which can be selectively cyclized to provide either the kinetic α-furanose or the thermodynamically favored ß-anomer. The method significantly expedites the synthesis of Remdesivir precursor GS-441524 after a subsequent Mn-catalyzed C-H oxidation and deoxycyanation.

The ability of carbon nanoparticles to increase transmembrane current of cations coincides with impaired synaptic neurotransmission.

Here, carbon nanodots synthesized from ß-alanine (Ala-CDs) and detonation nanodiamonds (NDs) were assessed using (1) radiolabeled excitatory neurotransmitters L-[14C]glutamate, D-[2,33H]aspartate, and inhibitory ones [3H]GABA, [3H]glycine for registration of their extracellular concentrations in rat cortex nerve terminals; (2) the fluorescent ratiometric probe NR12S and pH-sensitive probe acridine orange for registration of the membrane lipid order and synaptic vesicle acidification, respectively; (3) suspended bilayer lipid membrane (BLM) to monitor changes in transmembrane current. In nerve terminals, Ala-CDs and NDs increased the extracellular concentrations of neurotransmitters and decreased acidification of synaptic vesicles, whereas have not changed sufficiently the lipid order of membrane. Both nanoparticles, Ala-CDs and NDs, were capable of increasing the conductance of the BLM by inducing stable potential-dependent cation-selective pores. Introduction of divalent cations, Zn2+ or Cd2+ on the particles` application side (cis-side) increased the rate of Ala-CDs pore-formation in the BLM. The application of positive potential (+100 mV) to the cis-chamber with Ala-CDs or NDs also activated the insertion as compared with the negative potential (-100 mV). The Ala-CD pores exhibited a wide-range distribution of conductances between 10 and 60 pS and consecutive increase in conductance of each major peak by ~10 pS, which suggest the clustering of the same basic ion-conductive structure. NDs also formed ion-conductive pores ranging from 6 pS to 60 pS with the major peak of conductance at ~12 pS in cholesterol-containing membrane. Observed Ala-CDs and NDs-induced increase in transmembrane current coincides with disturbance of excitatory and inhibitory neurotransmitter transport in nerve terminals.

Synthetic Attempts Towards Eminent Anti-viral Candidates of SARS-CoV.

Severe Acute Respiratory Syndrome (SARS) aka SARS-CoV spread over southern China for the first time in 2002-2003 and history repeated again since last year and took away lives of more than two million people so far. On March 11, 2020 COVID-19 outbreak was officially declared as pandemic by World Health Organization (WHO). The entire world united to fight back against this ultimate destruction. Around 90 vaccines are featured against SARS-CoV-2 and more than 300 active clinical trials are underway by several groups and individuals. So far, no drugs have been currently approved that can completely eliminate the deadly coronavirus. The promising SARS-CoV-2 antiviral drugs are favipiravir, remdesivir, lopinavir, ribavirin and avifavir. In this review, we have discussed the synthetic approaches elaborately made so far by different groups and chemical companies all around the world towards top three convincing anti-viral drugs against SARS-CoV-2, which are favipiravir, remdesivir and lopinavir.

Design and synthesis of an oral prodrug alalevonadifloxacin for the treatment of MRSA infection.

Levonadifloxacin is a parenteral anti-MRSA benzoquinolizine antibacterial drug recently launched as, EMROK in India to treat acute bacterial skin and skin structure infections (ABSSSI) in hospitalized patients. As a step down therapy an oral form of levonadifloxacin with comparable PK/PD was needed because the levonadifloxacin exhibits very poor oral absorption. To improve the drugability in terms of oral absorption a pro-drug approach was evaluated. Structurally levonadifloxacin provides two sites amenable for ester or amide formation, a carboxyl function of benzoquinolizine pharmacophore and hydroxyl group on piperidine side chain. Several aliphatic, aromatic and amino acid esters of C-2 carboxylic acid, C-4-hydroxyl piperidine and double esters at both C-2, C-4 positions were synthesized. The cleavage of prodrugs was studied in vitro as well as in animal models to access their suitability as prodrug function. Among C-2 carboxylic ester prodrugs, daloxate (WCK 2320) showed highest cleavage in serum as well as in liver enzyme; however its stability in aqueous solution was unfavorable. In contrast, most of the esters at the hydroxyl group like propionyl ester (WCK 2305) and amino acid esters such as l-alanine (WCK 2349), l-valine (WCK 2630) were cleaved readily releasing active drug. Thus, indicating C-4-hydroxyl piperidine was amenable site for enzymatic cleavage over esters of C-2 carboxylic acid. Additionally, amino acid esters provided an opportunity to make salt, facilitating improved aqueous solubility. Methanesulfonate salt of l-alanine ester of levonadifloxacin (WCK 2349) was successfully developed and launched as oral prodrug alalevonadifloxacin (EMROK-O).

Synthesis and antiviral activity of fatty acyl conjugates of remdesivir against severe acute respiratory syndrome coronavirus 2 and Ebola virus.

We report here the synthesis, purification, and characterization of mono- and di-fatty acyl conjugates of remdesivir (RDV) and their in vitro antiviral activity against SAR-CoV-2, an Ebola virus transcription- and replication-competent virus-like particle (trVLP) system, and infectious Ebola virus. The most potent monofatty acyl conjugate was 4b, containing a 4-oxatetradecanolyl at the 3' position. Monofatty acyl conjugates, 3'-O-tetradecanoyl (4a) (IC50(VeroE6) = 2.3 µM; IC50(Calu3) = 0.24 µM), 3'-O-4-oxatetradodecanoyl (4b) (IC50(VeroE6) = 2.0 µM; IC50(Calu3) = 0.18 µM), and 3'-O-(12-ethylthiododecanoyl) (4e) (IC50(VeroE6) = 2.4 µM; IC50(Calu3) = 0.25 µM) derivatives exhibited less activity than RDV (IC50(VeroE6) = 0.85 µM; IC50(Calu3) = 0.06 µM) in both VeroE6 and Calu3 cells. Difatty acylation led to a significant reduction in the antiviral activity of RDV (as shown in conjugates 5a and 5b) against SARS-CoV-2 when compared with monofatty acylation (3a-e and 4a-e). About 77.9% of 4c remained intact after 4 h incubation with human plasma while only 47% of parent RDV was observed at the 2 h time point. The results clearly indicate the effectiveness of fatty acylation to improve the half-life of RDV. The antiviral activities of a number of monofatty acyl conjugates of RDV, such as 3b, 3e, and 4b, were comparable with RDV against the Ebola trVLP system. Meanwhile, the corresponding physical mixtures of RDV and fatty acids 6a and 6b showed 1.6 to 2.2 times less antiviral activity than the corresponding conjugates, 4a and 4c, respectively, against SARS-CoV-2 in VeroE6 cells. A significant reduction in viral RNA synthesis was observed for selected compounds 3a and 4b consistent with the IC50 results. These studies indicate the potential of these compounds as long-acting antiviral agents or prodrugs of RDV.

Design, synthesis, and biological evaluation of novel Bcr-AblT315I inhibitors incorporating amino acids as flexible linker.

Despite the success of imatinib in CML therapy through Bcr-Abl inhibition, acquired drug resistance occurs over time in patients. In particular, the resistance caused by T315I mutation remains a challenge in clinic. Herein, we embarked on a structural optimization campaign aiming at discovery of novel Bcr-Abl inhibitors toward T315I mutant based on previously reported dibenzoylpiperazin derivatives. We proposed that incorporation of flexible linker could achieve potent inhibition of Bcr-AblT315I by avoiding steric clash with bulky sidechain of Ile315. A library of 28 compounds with amino acids as linker has been developed and evaluated. Among them, compound AA2 displayed the most potent activity against Bcr-AblWT and Bcr-AblT315I, as well as toward Bcr-Abl driven K562 and K562R cells. Further investigations indicated that AA2 could induce apoptosis of K562 cells and down regulate phosphorylation of Bcr-Abl. In summary, the compounds with amino acid as novel flexible linker exhibited certain antitumor activities, providing valuable hints for the discovery of novel Bcr-Abl inhibitors to overcome T315I mutant resistance, and AA2 could be considered as a candidate for further optimization.

Discovery of novel and potent safinamide-based derivatives as highly selective hMAO-B inhibitors for treatment of Parkinson's disease (PD): Design, synthesis, in vitro, in vivo and in silico biological studies.

Up to date, the current clinical practice employs only symptomatic treatments for management of Parkinson's disease (PD) but unable to stop disease progression. The discovery of new chemical entities endowed with potent and selective human monoamine oxidase B (hMAO-B) inhibitory activity is a clinically relevant subject. Herein, a structural optimization strategy for safinamide (a well-known second generation hMAO-B inhibitor) afforded a series of thirty-six safinamide-derived new analogs (4aa-bj). Most compounds showed promising inhibitory activities against hMAO-B (>70% inhibition at a single dose concentration of 10 µM), with no apparent effect on hMAO-A at 100 µM. Moreover, while six compounds (4ak, 4as, 4az, 4be, 4bg, and 4bi) exhibited potent double-digit nanomolar activities over hMAO-B with IC50 values of 29.5, 42.2, 22.3, 18.8, 42.2, and 33.9 nM, respectively, three derivatives (4aq, 4at, and 4bf), possessing the same carboxamide moiety (2-pyrazinyl), showed the most potent single-digit nanomolar activities (IC50 = 9.7, 5.1, and 3.9 nM, respectively). Compound 4bf revealed an excellent selectivity index (SI > 25641) with a 29-fold increase compared to safinamide (SI > 892). A structure activity relationship along with molecular docking simulations provided insights into enzyme - inhibitor interactions and a rational for the observed activity. In an in vivo MPTP-induced mouse model of PD, oral administration of compound 4bf significantly protected nigrostriatal dopaminergic neurons as revealed by tyrosine hydroxylase staining and prevented MPTP-induced Parkinsonism as revealed by motor behavioral assays. Accordingly, we present compound 4bf as a novel, highly potent, and selective hMAO-B inhibitor with an effective therapeutic profile for relieving PD.

Mechanistic Insight into the Origin of Stereoselectivity in the Ribose-Mediated Strecker Synthesis of Alanine.

Enantioenriched amino acids are produced in a hydrolytic kinetic resolution of racemic aminonitriles mediated by chiral pentose sugars. Experimental kinetic and spectroscopic results combined with DFT computational studies and microkinetic modeling help to identify the nature of the intermediate species and provide insight into the stereoselectivity of their hydrolysis in the prebiotically relevant ribose-alanine system. These studies support a synergistic role for sugars and amino acids in the emergence of homochirality in biological molecules.

Development of rebamipide-loaded spray-dried microsphere using distilled water and meglumine: physicochemical characterization and pharmacokinetics in rats.

In this study, a novel rebamipide-loaded spray-dried microsphere (RSM) with enhanced drug solubility and oral bioavailability has been developed utilizing meglumine, an alkalizing agent. The influence of carriers on the drug solubility alone, and the solubility and dissolution of the drug in the RSM was investigated. Among the alkalizing agents and hydrophilic polymers tested, meglumine and polyvinyl alcohol (PVA) showed the highest drug solubility and dissolution rate, respectively. Many RSMs were manufactured with various amounts of meglumine and PVA using distilled water, and their drug solubility and dissolution were determined. The physicochemical properties, dissolution and pharmacokinetics of the chosen RSM in rats were assessed compared to the rebamipide powder and commercial tablet. Among the RSMs tested, the one composed of rebamipide, meglumine and PVA at a weight ratio of 3:1.75:6 showed the highest drug solubility and dissolution. This RSM with a smooth spherical form significantly decreased the particle size and modified the amorphous rebamipide. Furthermore, the drug solubility, dissolution, plasma concentrations, AUC and Cmax values of RSM were significantly higher than those of drug powder and commercial tablet. Thus, this RSN system developed with distilled water and meglumine is recommended as an oral water-soluble rebamipide-loaded pharmaceutical product.

Weinreb Amide Approach to the Practical Synthesis of a Key Remdesivir Intermediate.

Currently, remdesivir is the first and only FDA-approved antiviral drug for COVID-19 treatment. Adequate supplies of remdesivir are highly warranted to cope with this global public health crisis. Herein, we report a Weinreb amide approach for preparing the key intermediate of remdesivir in the glycosylation step where overaddition side reactions are eliminated. Starting from 2,3,5-tri-O-benzyl-d-ribonolactone, the preferred route consisting of three sequential steps (Weinreb amidation, O-TMS protection, and Grignard addition) enables a high-yield (65%) synthesis of this intermediate at a kilogram scale. In particular, the undesirable PhMgCl used in previous methods was successfully replaced by MeMgBr. This approach proved to be suitable for the scalable production of the key remdesivir intermediate.

Practical Remdesivir Synthesis through One-Pot Organocatalyzed Asymmetric (S)-P-Phosphoramidation.

Remdesivir, an inhibitor of RNA-dependent RNA polymerase developed by Gilead Sciences, has been used for the treatment of COVID-19. The synthesis of remdesivir is, however, challenging, and the overall cost is relatively high. Particularly, the stereoselective assembly of the P-chirogenic center requires recrystallization of a 1:1 isomeric p-nitrophenylphosphoramidate mixture several times to obtain the desired diastereoisomer (39%) for further coupling with the d-ribose-derived 5-alcohol. To address this problem, a variety of chiral bicyclic imidazoles were synthesized as organocatalysts for stereoselective (S)-P-phosphoramidation employing a 1:1 diastereomeric mixture of phosphoramidoyl chloridates as the coupling reagent to avoid a waste of the other diastereomer. Through a systematic study of different catalysts at different temperatures and concentrations, a mixture of the (S)- and (R)-P-phosphoramidates was obtained in 97% yield with a 96.1/3.9 ratio when 20 mol % of the chiral imidazole-cinnamaldehyde-derived carbamate was utilized in the reaction at -20 °C. A 10-g scale one-pot synthesis via a combination of (S)-P-phosphoramidation and protecting group removal followed by one-step recrystallization gave remdesivir in 70% yield and 99.3/0.7 d.r. The organocatalyst was recovered in 83% yield for reuse, and similar results were obtained. This one-pot process offers an excellent opportunity for industrial production of remdesivir.

Peripheral Selective Oxadiazolylphenyl Alanine Derivatives as Tryptophan Hydroxylase 1 Inhibitors for Obesity and Fatty Liver Disease.

Tryptophan hydroxylase 1 (TPH1) has been recently suggested as a promising therapeutic target for treating obesity and fatty liver disease. A new series of 1,2,4-oxadiazolylphenyl alanine derivatives were identified as TPH1 inhibitors. Among them, compound 23a was the most active in vitro, with an IC50 (half-maximal inhibitory concentration) value of 42 nM, showed good liver microsomal stability, and showed no significant inhibition of CYP and hERG. Compound 23a inhibited TPH1 in the peripheral tissue with limited BBB penetration. In high-fat diet-fed mice, 23a reduced body weight gain, body fat, and hepatic lipid accumulation. Also, 23a improved glucose intolerance and energy expenditure. Taken together, compound 23a shows promise as a therapeutic agent for the treatment of obesity and fatty liver diseases.

Tackling COVID-19 Using Remdesivir and Favipiravir as Therapeutic Options.

The human world is currently influenced largely by the outbreak of pandemic COVID-19. At this moment, most researchers focus on developing treatment strategies and measures to work against COVID-19. Treatment strategies specific for COVID-19 are lacking. This article provides an overview of the life cycle and routes of transmission of SARS-CoV-2. The therapeutic effects of two drugs [i. e., remdesivir (RDV) and favipiravir (FPV)] which can potentially tackle COVID-19 are discussed based on current published data. This review can serve as a reference for future studies.

Prebiotic synthesis of cysteine peptides that catalyze peptide ligation in neutral water.

Peptide biosynthesis is performed by ribosomes and several other classes of enzymes, but a simple chemical synthesis may have created the first peptides at the origins of life. α-Aminonitriles-prebiotic α-amino acid precursors-are generally produced by Strecker reactions. However, cysteine's aminothiol is incompatible with nitriles. Consequently, cysteine nitrile is not stable, and cysteine has been proposed to be a product of evolution, not prebiotic chemistry. We now report a high-yielding, prebiotic synthesis of cysteine peptides. Our biomimetic pathway converts serine to cysteine by nitrile-activated dehydroalanine synthesis. We also demonstrate that N-acylcysteines catalyze peptide ligation, directly coupling kinetically stable-but energy-rich-α-amidonitriles to proteinogenic amines. This rare example of selective and efficient organocatalysis in water implicates cysteine as both catalyst and precursor in prebiotic peptide synthesis.

Cyanoamidine Cyclization Approach to Remdesivir's Nucleobase.

We report an alternative approach to the unnatural nucleobase fragment seen in remdesivir (Veklury). Remdesivir displays broad-spectrum antiviral activity and is currently being evaluated in Phase III clinical trials to treat patients with COVID-19. Our route relies on the formation of a cyanoamidine intermediate, which undergoes Lewis acid-mediated cyclization to yield the desired nucleobase. The approach is strategically distinct from prior routes and could further enable the synthesis of remdesivir and other small-molecule therapeutics.

Visible-light-driven amino acids production from biomass-based feedstocks over ultrathin CdS nanosheets.

Chemical synthesis of amino acids from renewable sources is an alternative route to the current processes based on fermentation. Here, we report visible-light-driven amination of biomass-derived α-hydroxyl acids and glucose into amino acids using NH3 at 50 °C. Ultrathin CdS nanosheets are identified as an efficient and stable catalyst, exhibiting an order of magnitude higher activity towards alanine production from lactic acid compared to commercial CdS as well as CdS nanoobjects bearing other morphologies. Its unique catalytic property is attributed mainly to the preferential formation of oxygen-centered radicals to promote α-hydroxyl acids conversion to α-keto acids, and partially to the poor H2 evolution which is an undesired side reaction. Encouragingly, a number of amino acids are prepared using the current protocol, and one-pot photocatalytic conversion of glucose to alanine is also achieved. This work offers an effective catalytic system for amino acid synthesis from biomass feedstocks under mild conditions.

Catalytic Asymmetric Synthesis of the anti-COVID-19 Drug Remdesivir.

The catalytic asymmetric synthesis of the anti-COVID-19 drug Remdesivir has been realized by the coupling of the P-racemic phosphoryl chloride with protected nucleoside GS441524. The chiral bicyclic imidazole catalyst used is crucial for the dynamic kinetic asymmetric transformation (DyKAT) to proceed smoothly with high reactivity and excellent stereoselectivity (96 % conv., 22:1 SP :RP ). Mechanistic studies showed that this DyKAT is a first-order visual kinetic reaction dependent on the catalyst concentration. The unique chiral bicyclic imidazole skeleton and carbamate substituent of the catalyst are both required for the racemization process, involving the phosphoryl chloride, and subsequent stereodiscriminating step. A 10 gram scale reaction was also conducted with comparably excellent results, showing its potential for industrial application.