Design and synthesis of vidarabine prodrugs as antiviral agents

Synthesis and antiviral effect of phosphamide modified vidarabine for treating HSV 1 infections

Vidarabine (ARA) was one of the earliest marine-related compounds to be used clinically for antiviral therapy, however, its fast metabolism is the main defect of this drug. To overcome this, we designed and synthesized a group of phosphamide-modified ARA compounds using ProTide technology. With a phosphamide modification, these compounds could become the substrate of specific phospholipase enzymes expressed in the liver. Among all 16 synthesized compounds, most showed stronger activity against herpes simplex virus type 1 (HSV-1) than ARA (EC₅₀ of approximately 10 μM). The top three compounds were compound 2 (EC₅₀ = 0.52 ± 0.04 μM), compound 6 (EC₅₀ = 1.05 ± 0.09 μM) and compound 15 (EC₅₀ = 1.18 ± 0.08 μM) (about 2 times higher than Sp type compound 2). This study provides evidence for use of the phosphamide modification, which could give ARA higher activity and liver cell targeting.

Application of carbohydrates in approved small molecule drugs: A review

Carbohydrates are an important energy source and play numerous key roles in all living organisms. Carbohydrates chemistry involved in diagnosis and treatment of diseases has been attracting increasing attention. Carbohydrates could be one of the major focuses of new drug discovery. Currently, however, carbohydrate-containing drugs account for only a small percentage of all drugs in clinical use, which does not match the important roles of carbohydrates in the organism. In other words, carbohydrates are a relatively untapped source of new drugs and therefore may offer exciting novel therapeutic opportunities. Here, we presented an overview of the application of carbohydrates in approved small molecule drugs and emphasized and evaluated the roles of carbohydrates in those drugs. The potential development direction of carbohydrate-containing drugs was presented after summarizing the advantages and challenges of carbohydrates in the development of new drugs.

Fludarabine Inhibits Infection of Zika Virus, SFTS Phlebovirus, and Enterovirus A71

Viral infections are one of the leading causes in human mortality and disease. Broad-spectrum antiviral drugs are a powerful weapon against new and re-emerging viruses. However, viral resistance to existing broad-spectrum antivirals remains a challenge, which demands development of new broad-spectrum therapeutics. In this report, we showed that fludarabine, a fluorinated purine analogue, effectively inhibited infection of RNA viruses, including Zika virus, Severe fever with thrombocytopenia syndrome virus, and Enterovirus A71, with all IC₅₀ values below 1 μM in Vero, BHK21, U251 MG, and HMC3 cells. We observed that fludarabine has shown cytotoxicity to these cells only at high doses indicating it could be safe for future clinical use if approved. In conclusion, this study suggests that fludarabine could be developed as a potential broad-spectrum anti-RNA virus therapeutic agent.

Gaining insight into irrational off-label use of vidarabine through analysis of a spontaneous reporting system in China

WHAT IS KNOWN AND OBJECTIVE

Although superseded by other antiviral agents in many Western countries, vidarabine is still widely used in some countries, including China; hence, the extent and appropriateness of vidarabine prescriptions in children require better characterization. This study examined the rationale, extent, and health risks associated with irrational off-label vidarabine use in China.

METHODS

Data used in the study were extracted from a multi-provincial joint adverse drug reactions monitoring platform from 2002 to 2018. Descriptive statistics were used to analyse the characteristics of individual case safety reports (ICSRs) related to vidarabine use.

RESULTS AND DISCUSSION

Among 2772 individual ICSRs related to vidarabine, 2223 (80.19%) cases occurred in patients aged 0-9. In all patients, the median age and interquartile range were 2 (0-6). Although most adverse events were mild, five deaths were recorded, all in children below 7 years of age. Paediatric use is the most prominent off-label use of vidarabine. Additionally, several other irrational off-label uses were identified, including 218 (7.86%) cases of overdosing and numerous applications beyond the approved indications, dosages, routes of administration, and solvents.

WHAT IS NEW AND CONCLUSION

Data indicate that vidarabine was mainly prescribed for suspected common viral infections in paediatric patients, demonstrating serious inappropriate off-label uses. The problem was further complicated by the lack of sufficient information regarding safety, efficacy, and dosing regimens in children, as well as by several additional risk factors such as inappropriate solvents, routes of administration, and overdose. In the case of children, the physicians' lack of understanding of antiviral activities and compassionate prescriptions were mainly responsible for drug overuse. The health risks associated with the paediatric use of vidarabine in China require greater attention and further investigation.

Highlights of marine natural products having parallel scaffolds found from marine-derived bacteria, sponges, and tunicates

Marine-derived bacteria are a prolific source of a wide range of structurally diverse natural products. This review, dedicated to Professor William Fenical, begins by showcasing many seminal discoveries made at the University of California San Diego from marine-derived actinomycetes. Discussed early on is the 20-year journey of discovery and advancement of the seminal actinomycetes natural product salinosporamide A into Phase III anticancer clinical trials. There are many fascinating parallels discussed that were gleaned from the comparative literature of marine sponge, tunicate, and bacteria-derived natural products. Identifying bacterial biosynthetic machinery housed in sponge and tunicate holobionts through both culture-independent and culture-dependent approaches is another important and expanding subject that is analyzed. Work reviewed herein also evaluates the hypotheses that many marine invertebrate-derived natural products are biosynthesised by associated or symbiotic bacteria. The insights and outcomes from metagenomic sequencing and synthetic biology to expand molecule discovery continue to provide exciting outcomes and they are predicted to be the source of the next generation of novel marine natural product chemical scaffolds.

Metabolomic tools used in marine natural product drug discovery

Introduction: The marine environment is a very promising resource for natural product research, with many of these reaching the market as new drugs, especially in the field of cancer therapy as well as the drug discovery pipeline for new antimicrobials. Exploitation for bioactive marine compounds with unique structures and novel bioactivity such as the isoquinoline alkaloid; trabectedin, the polyether macrolide; halichondrin B, and the peptide; dolastatin 10, requires the use of analytical techniques, which can generate unbiased, quantitative, and qualitative data to benefit the biodiscovery process. Metabolomics has shown to bridge this understanding and facilitate the development of new potential drugs from marine sources and particularly their microbial symbionts.Areas covered: In this review, articles on applied secondary metabolomics ranging from 1990-2018 as well as to the last quarter of 2019 were probed to investigate the impact of metabolomics on drug discovery for new antibiotics and cancer treatment.Expert opinion: The current literature review highlighted the effectiveness of metabolomics in the study of targeting biologically active secondary metabolites from marine sources for optimized discovery of potential new natural products to be made accessible to a R&D pipeline.

A novel nucleoside rescue metabolic pathway may be responsible for therapeutic effect of orally administered cordycepin

Although adenosine and its analogues have been assessed in the past as potential drug candidates due to the important role of adenosine in physiology, only little is known about their absorption following oral administration. In this work, we have studied the oral absorption and disposition pathways of cordycepin, an adenosine analogue. In vitro biopharmaceutical properties and in vivo oral absorption and disposition of cordycepin were assessed in rats. Despite the fact that numerous studies showed efficacy following oral dosing of cordycepin, we found that intact cordycepin was not absorbed following oral administration to rats. However, 3′-deoxyinosine, a metabolite of cordycepin previously considered to be inactive, was absorbed into the systemic blood circulation. Further investigation was performed to study the conversion of 3′-deoxyinosine to cordycepin 5′-triphosphate in vitro using macrophage-like RAW264.7 cells. It demonstrated that cordycepin 5′-triphosphate, the active metabolite of cordycepin, can be formed not only from cordycepin, but also from 3′-deoxyinosine. The novel nucleoside rescue metabolic pathway proposed in this study could be responsible for therapeutic effects of adenosine and other analogues of adenosine following oral administration. These findings may have importance in understanding the physiology and pathophysiology associated with adenosine, as well as drug discovery and development utilising adenosine analogues.

Synthesis and cytotoxic evaluation of apioarabinofuranosyl pyrimidines

In view of the potent anticancer activity of the d-arabino-configured cytosine nucleoside (ara-C), apioarabinofuranosyl pyrimidine nucleosides were designed and synthesized from d-ribose as starting material. The synthetic strategy signifies that tosylation followed by in situ cyclization, one-pot controlled oxidative cleavage and acetylation by Pb(OAc)₄ , stereoselective nucleobase condensation, inversion of hydroxyl group and uracil group converted to cytosine as the key steps. Synthesized apioarabinofuranosyl pyrimidine nucleosides were tested using breast, colon, and ovarian cancer cell lines. However, only compound 19a, 19b, and 22b have a moderate growth-suppressive effect against the luminal A breast cancer cell line MCF7.

Amino Acids in the Development of Prodrugs

Although drugs currently used for the various types of diseases (e.g., antiparasitic, antiviral, antibacterial, etc.) are effective, they present several undesirable pharmacological and pharmaceutical properties. Most of the drugs have low bioavailability, lack of sensitivity, and do not target only the damaged cells, thus also affecting normal cells. Moreover, there is the risk of developing resistance against drugs upon chronic treatment. Consequently, their potential clinical applications might be limited and therefore, it is mandatory to find strategies that improve those properties of therapeutic agents. The development of prodrugs using amino acids as moieties has resulted in improvements in several properties, namely increased bioavailability, decreased toxicity of the parent drug, accurate delivery to target tissues or organs, and prevention of fast metabolism. Herein, we provide an overview of models currently in use of prodrug design with amino acids. Furthermore, we review the challenges related to the permeability of poorly absorbed drugs and transport and deliver on target organs.

A practical synthesis of xylo- and arabinofuranoside precursors by diastereoselective reduction using Corey-Bakshi-Shibata catalyst

The Corey-Bakshi-Shibata (CBS) catalyst provides an efficient mechanism to reduce ketones and achieve desired enantiopure alcohols. Herein, the diastereoselective reduction of C-2' and C-3'-keto ribofuranoside derivatives to the corresponding arabino- and xylofuranosides in greater than 95% diastereomeric excess is reported. The stereo-directed substitution with an azido group as well as the synthesis of prodrugs cytarabine and vidarabine are also described. The reported strategy offers superior diastereoselectivity, shorter reaction times, and obviates cooling required with comparable protocols involving achiral reductants.

Toxicity and Potential Pharmacological Activities in the Persian Gulf Venomous Sea Anemone, Stichodactyla haddoni

Numerous proteins and peptides in venomous marine animals are potentially active molecules with pharmacological properties. Particular condition of the Persian Gulf as a closed ecosystem is a good opportunity to study of biological activities and toxicity of venomous animals. In this study, Stichodactyla haddoni (S. haddoni), a sea anemone, selected to tracing for possible pharmaceutical agents and toxicological characterization. Analgesic, edematogenic, dermonecrotic, LD50, phospholipase, and proteolytic activities of the venom were estimated. LD50 was recorded at 675 μg by intraperitoneal injection. Analgesic activitiy of crude venom on Balb/c mice at both 100 and 150 µg were dose dependent as a linear trend. Three folds increase of activity was seen at both 100 and 150 µg after 240 min comparing to activity of morphine at 200 µg. The crude venom at amount of 0.23 µg produced 50% hemolysis. The highest edematogenic activity was seen on Balb/c mice just two hours after injection for both 168 µg (157%) and 335 µg (247%). The crude venom at 675 µg made 4 mm inflammation area on rabbit skin after 3 h but the amount of 1000 µg induced 8 mm necrosis area. Potent analgesic activity of the venom was seen below its toxic dose that was very greater than the other sea anemones in the other geographical areas. The results indicate that a persistent edematogenic activity could be happened after envenomation. Instant potent edematogenic and rapid dermonecrotic activity were significant phenomena. HD50 at 0.23 µg indicates that a very potent hemolytic agent exists in the venom. The results would also be of high value to better management of envenomation. This study confirmed the great value of further studies on the Persian Gulf S. haddoni venom.

Phospholipid derivatives of cladribine and fludarabine: synthesis and biological properties

Phospholipid derivatives of anticancer nucleosides cladribine and fludarabine (F-ara-A) bearing 1,2- and 1,3-diacylglycerol moieties have been prepared by the H-phosphonate approach using 1,1,3,3-tetraisopropyldisiloxane-1,3-diyl protecting group for cladribine and a combination of tert-butyldimethylsilyl and levulinyl protecting groups for 2-fluoroadenine nucleosides. The synthesized conjugates exhibited lower in vitro antiproliferative activity against human tumor cell lines in comparison with the same concentrations of the parent cladribine and fludarabine phosphate. In the course of biokinetic study, it was found that intragastric administration of phospholipid F-ara-A derivatives to Wistar rats and ICR outbred male mice led to a slow release of F-ara-A into the bloodstream, a smooth increase in nucleoside concentration, and prolonged serum circulation of liberated nucleoside. The oral bioavailability of F-ara-A from 1,2-dimyristoylglycerophosphate derivative 29 was similar to its oral bioavailability from fludarabine phosphate.

Redesigning the synthesis of vidarabine via a multienzymatic reaction catalyzed by immobilized nucleoside phosphorylases

The comparison between the biocatalyzed synthesis of araA here described and the chemical synthesis of this nucleoside showed that the enzymatic route is superior (less steps, milder conditions and reagents, easier downstream, lower E-factor).

Marketed marine natural products in the pharmaceutical and cosmeceutical industries: tips for success

The marine environment harbors a number of macro and micro organisms that have developed unique metabolic abilities to ensure their survival in diverse and hostile habitats, resulting in the biosynthesis of an array of secondary metabolites with specific activities. Several of these metabolites are high-value commercial products for the pharmaceutical and cosmeceutical industries. The aim of this review is to outline the paths of marine natural products discovery and development, with a special focus on the compounds that successfully reached the market and particularly looking at the approaches tackled by the pharmaceutical and cosmetic companies that succeeded in marketing those products. The main challenges faced during marine bioactives discovery and development programs were analyzed and grouped in three categories: biodiversity (accessibility to marine resources and efficient screening), supply and technical (sustainable production of the bioactives and knowledge of the mechanism of action) and market (processes, costs, partnerships and marketing). Tips to surpass these challenges are given in order to improve the market entry success rates of highly promising marine bioactives in the current pipelines, highlighting what can be learned from the successful and unsuccessful stories that can be applied to novel and/or ongoing marine natural products discovery and development programs.

Efficient conversion of furfuryl alcohol into alkyl levulinates catalyzed by an organic-inorganic hybrid solid acid catalyst

A clean, facile, and environment-friendly catalytic method has been developed for the conversion of furfuryl alcohol into alkyl levulinates making use of the novel solid catalyst methylimidazolebutylsulfate phosphotungstate ([MIMBS]₃PW₁₂O₄₀). The solid catalyst is an organic-inorganic hybrid material, which consists of an organic cation and an inorganic anion. A study for optimizing the reaction conditions such as the reaction time, the temperature and the catalyst loading has been performed. Under optimal conditions, a high n-butyl levulinate yield of up to 93 % is obtained. Furthermore, the kinetics of the reaction pathways and the mechanism for the alcoholysis of furfuryl alcohol are discussed. This method is environmentally benign and economical for the conversion of biomass-based derivatives into fine chemicals.

Biodegradable protections for nucleoside 5'-monophosphates: comparative study on the removal of O-acetyl and O-acetyloxymethyl protected 3-hydroxy-2,2-bis(ethoxycarbonyl)propyl groups

The applicability of 3-acetyloxy-2,2-bis(ethoxycarbonyl)propyl and 3-acetyloxymethoxy-2,2-bis(ethoxycarbonyl)propyl groups as biodegradable phosphate protecting groups for nucleoside 5'-monophosphates has been studied in a HEPES buffer at pH 7.5. Enzymatic deacetylation with porcine carboxyesterase triggers the removal of the resulting 3-hydroxy-2,2-bis(ethoxycarbonyl)propyl and 3-hydroxymethoxy-2,2-bis(ethoxycarbonyl)propyl groups by retro-aldol condensation and consecutive half acetal hydrolysis and retro-aldol condensation, respectively. The kinetics of these multistep deprotection reactions have been followed by HPLC, using appropriately protected thymidine 5'-monophosphates as model compounds. The enzymatic deacetylation of the 3-acetyloxymethoxy-2,2-bis(ethoxycarbonyl)propyl 5'-triester (2) is 25-fold faster than the deacetylation of its 3-acetyloxy-2,2-bis(ethoxycarbonyl)propyl-protected counterpart 1, and the difference in the deacetylation rates of the resulting diesters, 12b and 12a, is even greater. With 2, conversion to thymidine 5'-monophosphate (5'-TMP) is quantitative, while conversion of 1 to 5'-TMP is accompanied by formation of thymidine. Consistent with the preceding observations, quantitative release of 5'-TMP from 2 has been shown to take place in a whole cell extract of human prostate cancer cells.