Shikonin and its derivatives: a patent review

Introduction: Shikonin and its derivatives are the main components of red pigment extracts from Lithospermum erythrorhizon, whose medicinal properties have been confirmed for a long history, and have aroused great interest as the hallmark molecules responsible for their significant biological activities, especially for their striking anticancer effects. Areas covered: Areas covered in this paper include a review of the total synthesis, biological effects and mechanisms of shikonin and its derivatives for their anticancer activities in the past decade, basing on literature and patents. The current state and problems are also discussed. Expert opinion: At present, screening for anticancer shikonin derivatives is based on cellular level to find compounds with stronger cytotoxicity. Though several compounds have been discovered with striking cytotoxicity in vitro, however, no selectivity was observed and undoubtedly, the further outcomes have been disappointing because of their great damage to normal cells. Meanwhile, the presumed mechanisms of action are also established in terms of their cytotoxicity. From a pharmacological point of view, most of the shikonin derivatives are at an early stage of their development, and thus it is difficult to determine the exact effectiveness in cancer treatment. With research in this field going deeper, it can be expected that, despite the difficulties, shikonin derivatives as potential anticancer agents will soon follow.     

Recent progress in therapeutic applications of chalcones

Introduction: Chalcones are a group of plant-derived polyphenolic compounds belonging to the flavonoids family that possess a wide variety of cytoprotective and modulatory functions, which may have therapeutic potential for multiple diseases. Their physicochemical properties seem to define the extent of their biological activity.

Areas covered: A comprehensive synopsis of recent patent literature (2005 – 2011) describing chalcones and their derivatives on selected activities (e.g., anti-inflammatory, antimitotic, cytotoxic, antioxidant, anti-infection) is provided in this paper. Synthesis, combinatorial techniques, biological evaluation in vitro/in vivo, and new biological assays are discussed. In addition to selected biological data, a wide range of pharmaceutical applications and pharmaceutical compositions are also summarized.

Expert opinion: Several natural and synthetic chalcones and their derivatives appear as promising anti-inflammatory and anticancer activities. Their clinical evaluation will be critical to assess their therapeutic utility. Those for which the mechanism of action is well defined can serve as lead compounds for the design of new, more promising molecules.     

Coumarin derivatives: an updated patent review (2012 – 2014)

Introduction: Coumarins belong to the benzopyrones family. They are naturally plant-derived and synthetically taken polyphenolic substances, presenting a wide variety of biological activities and behaviours, supporting their use as therapeutic agents for multiple diseases. Their structural characteristics correlated to physicochemical properties seem to define the extent of the biological activity.

Areas covered: Recent patent publications (2012 – 2014), describing coumarins and their derivatives are analyzed. Synthesis, hybridization techniques and biological evaluation in vitro/in vivo, for example, antimitotic, antiviral, anticancer, cytotoxic, anti-acne and antioxidant coumarin macromolecule polymer agents are included. Furthermore, a wide range of pharmaceutical applications and pharmaceutical compositions are also summarized.

Expert opinion: Several natural and synthetic coumarins, hybrids and derivatives appear to have promising anticancer-antitumor activities. Their clinical evaluation will be critical to assess therapeutic utility. The compounds for which the mechanism of action is well defined can serve as lead compounds for the design of new more potent molecules.     

New substituted benzimidazole derivatives: a patent review (2013 – 2014)

Introduction: The benzimidazole nucleus is found in a variety of naturally occurring compounds and is of significant importance in medicinal chemistry. Owing to its conspicuous pharmacological properties, benzimidazoles have become an important pharmacophore and sub-structure in drug design and have been screened for a wide range of biological activities.

Areas covered: Areas covered in this paper include a review of the biological effects, mechanisms and synthesis of benzimidazole derivatives in the past 2 years based on patents. The patent databases Scifinder and esp@cenet were used to locate patent applications that were published between 2013 to present. Information from articles published is also included.

Expert opinion: Benzimidazole derivatives are remarkably effective compounds to many diseases and may have the potential to be the first effective therapy against Ebola virus. Therefore, it is of great importance to develop specific design software and sustainable industrial synthetic routes for the development of effective and clinically relevant benzimidazole compounds.     

Coumarin derivatives: an updated patent review (2015-2016)

Introduction: Coumarins belong to the benzopyrone family. They are naturally plant-derived or synthetically obtained substances, presenting a wide variety of biological activities, offering an extented therapeutic profile. Their structural characteristics correlated to physicochemical properties define their pleiotropic biological responses.

Areas covered in this review: Recent patent publications (2015–2016), describing coumarins and their derivatives are analyzed. Synthesis, biological evaluations in vitro /in vivo e.g. antiviral, anticancer, cytotoxic, antioxidant, anti-inflammmatory protocols are included. Furthermore, several pharmaceutical applications and pharmaceutical compositions are also described.

Expert opinion: Several synthetic coumarins, hybrids and derivatives (azoles, sulfonyl, furazan, pyrazole etc) have been found to possess promising anticancer, antitumor anti-proliferative activities. Their clinical evaluation will be critical to assess therapeutic utility. The compounds for which the mechanism of action is well defined can serve as lead compounds for the design of new more potent molecules.     

The design and development of imidazothiazole–chalcone derivatives as potential anticancer drugs

Introduction: Imidazothiazole derivatives have long been therapeutically used for the treatment of various diseases. In recent years, the imidazothiazole and chalcone moieties have emerged as important pharmacophores in the development of antitumor agents. Imidazothiazole–chalcone conjugates can be accessed by covalently binding these two powerful pharamacophore units. These conjugates are known to exhibit a wide range of biological properties, including anticancer, antimicrobial, anti-inflammatory and immunosuppressive activities. Their promising biological profile and easy synthetic accessibility have triggered investigations directed at the design and development of new imidazothiazole–chalcone conjugate derivatives as potential chemotherapeutics.

Areas covered: The present review focuses on recent reports of the syntheses and anticancer properties of various imidazothiazoles, chalcones and imidazothiazole-linked chalcone conjugates. Furthermore, the authors discuss the structure–activity relationships (SAR) of imidazothiazoles and chalcones and their conjugates as new antitumor agents, as well as in vitro and in vivo evaluation, clinical use and their future therapeutic applications.

Expert opinion: A large number of imidazothiazoles, chalcones and a new series of imidazothiazole–chalcone conjugates possess potent anticancer activity that could be further developed as drug candidates. Imidazothiazole-based conjugates could also display synergistic effect, and still there is a need to use the drug combinations permitting lower dose and development of new generation of drugs. Despite encouraging observed results for their response to tumors in clinical studies, full characterization of their toxicity is further required for their clinical usage as safe drugs for the treatment of cancer.     

Therapeutic potential of oxazole scaffold: a patent review (2006–2017)

ABSTRACT

Introduction: Oxazoles are oxygen and nitrogen containing five membered heterocyclic ring systems that are present in various anticancer, antimicrobial, antihyperglycemic, anti-inflammatory agents etc. of natural origin. These pharmacologically active oxazole derivatives have attracted numerous researchers to explore this scaffold for the design and development of newer potential therapeutic agents. A large number of synthetic oxazole containing molecules have been reported over the period that exhibited wide spectrum of pharmacological profiles. Some of them have shown promising therapeutic potential and have qualified for both preclinical and clinical evaluations.

Areas covered: In this review, the patents (published during 2006–2017) focusing on the biological potential of oxazoles have been covered. Therapeutic applications and various techniques/assays employed for the in vitro/in vivo evaluation of patented derivatives have been discussed majorly.

Expert opinion: Chemically oxazole offers three positions for substitution. These substituted oxazole derivatives of natural as well as synthetic origin have numerous pharmacological applications including anticancer, anti-Alzheimer’s, anti-hyperglycemic, anti-inflammatory, antibacterial etc. Their pharmacological actions are mainly mediated through enzyme/receptor involved in the particular disease. The flexible nature of this ligand for various molecular level targets (enzyme/receptor) make this heterocylce an attractive scaffold for development of effective and clinically relevant oxazole containing therapeutic agents.     

Pyrazine derivatives: a patent review (2008 – present)

Introduction: Pyrazines derivatives are well-known and important two-nitrogen-containing six-membered ring aromatic heterocyclic compounds and can carry substituents at one or more of the four ring carbon atoms. Pyrazines are a class of compounds that occur in nature and various methods have been worked out for their synthesis. A large number of pyrazine derivatives have been found to possess diverse pharmacological properties, which has caused an increasing interest by researchers in this core.

Area covered: This review provides a comprehensive review of the pyrazines derivatives patented between the years 2008 to 2012 as potential active compounds. The patent databases SciFinder and esp@cenet were used to locate patent applications that were published between 2008 to present. Information from articles published was also included.

Expert opinion: The diversity of pyrazines derivatives found in organisms in nature with different applications began to arouse the interest of research in this nucleus. The pyrazines derivatives have numerous prominent pharmacological effects, such as antibacterial, antifungal, antimycobacterial, anti-inflammatory, analgesic, anticancer for different types, antidiabetic, treatment for arteriosclerosis, antiviral. It's the time to conduct further studies aimed at rationalizing the biological activities found in order to develop more effective and clinically interesting compounds.     

Pharmacophore modeling technique applied for the discovery of proteasome inhibitors

Introduction: The 26S proteasome has many important roles in the biological functions of the cells, and proteasome inhibitors have multiple and complex activities on cells. These compounds can be natural or synthesized. Most synthetic derivatives have been rationally designed, synthesized and optimized to obtain the best selectivity and increase the activity. The design of chemical entities with desired molecular identification, which plays an important role in biological systems, is provided by pharmacophore modeling. Indeed, pharmacophore models can be established either in a ligand-based manner or in a receptor-based manner.

Areas covered: The authors discuss the application of pharmacophore modeling techniques to proteasome inhibitors development. Furthermore, the article reviews the classification of the currently discovered proteasome inhibitors where the principal mechanism of action and clinical application are represented.

Expert opinion: In the era of new drug development, database of compounds should be thoroughly evaluated with a combination of methods that consider both pharmacophore- and ligand-based virtual screening. The concept of pharmacophore helps to discover new active compounds and to evaluate their activity. The nature of proteasome inhibitor pharmacophore affects the secondary active-site specificity; indeed, increasing specificity decreases the cytotoxicity of the proteasome inhibitors. It is hypothesized that the balanced simultaneous modulation of a few druggable targets may have superior efficacy and fewer side effects than single-target or combination therapies for the treatment of human cancers. The discovery of new compounds should aim to find more active compounds that improve the compliance of patients.     

An update on benzofuran inhibitors: a patent review

ABSTRACT

Introduction: Benzofuran is a fundamental unit in numerous bioactive heterocycles. They have attracted chemists and medical researchers due to their broad range of biological activity, where some of them possess unique anticancer, antitubercular, antidiabetic, anti-Alzheimer and anti-inflammatory properties. The benzofuran nucleus is present in a huge number of bioactive natural and synthetic compounds. Benzofuran derivatives have potent applications in pharmaceuticals, agriculture, and polymers. The recent developments considering the biological activities of benzofuran compounds are reported. They have a vital role as pronounced inhibitors against a number of diseases, viruses, fungus, microbes, and enzymes.

Areas covered: This review covers the recent developments of biological activities of benzofurans during the period 2014–2019. The covered areas here comprised antimicrobial, anti-inflammatory, antitumor, antitubercular, antidiabetic, anti-Alzheimer, antioxidant, antiviral, vasorelaxant, anti-osteoporotic and enzyme inhibitory activities.

Expert opinion: In addition to the already commercialized 34 benzofurans-based drugs in the market, this chapter outlines several potent benzofuran derivatives that may be useful as potential pro-drugs. It is also focused on providing details of SAR and the effect of certain functional groups on the activity of the benzofuran compounds. The presence of -OH, -OMe, sulfonamide, or halogen contributed greatly to increasing the therapeutic activities comparing with reference drugs.     

Combretastatin-based compounds with therapeutic characteristics: a patent review

ABSTRACT

Introduction: Combretastatins represent a potent class of phenolic-stilbene natural products that function as colchicine binding site inhibitors of tubulin polymerization and have been advanced as promising anticancer lead compounds. Among them, combretastatin A-4 is the most potent lead molecule due to its broad spectrum cytotoxicity against a variety of tumors. However, low water solubility due to its high lipophilic nature and inter-conversion of olefinic double bond from more active cis to less active trans-conformation poses limitations to its clinical utility. However, different approaches including prodrugs, salt formations, structural modifications, prevention of inter-conversion of the olefinic bond and changes to the substitution pattern on the rings of combretastatin A-4 were investigated and successfully resulted in different combretastatin-based molecules that demonstrated varying levels of potency against different types of tumors during their in-vitro and in-vivo studies.

Areas covered: This review covers the patents over a period of 2008–2018.

Expert opinion: Molecular hybridization and prodrug designing imparted multi-targeted actions to combretastatin derivatives. Currently, various combretastatin derivatives are under clinical trials. These derivatives could be used to treat disorders other than cancer, due to their vascular disrupting action.     

Chloroquine-containing compounds: a patent review (2010 – 2014)

Introduction: Chloroquine (CQ) has been well known for its antimalarial effects since World War II. However, it is gradually being phased out from clinical use against malaria due to emergence of CQ-resistant Plasmodium falciparum strains. Besides low cost and tolerability, ongoing research has revealed interesting biochemical properties of CQ that have inspired its repurposing/repositioning in the management of various infectious/noninfectious diseases. Consequently, several novel compounds and compositions based on its scaffold have been studied and patented.

Areas covered: In this review, patents describing CQ and its derivatives/compositions over the last 5 years are analyzed. The review highlights the rationale, chemical structures, biological evaluation and potential therapeutic application of CQ, its derivatives and compositions.

Expert opinion: Repurposing efforts have dominantly focused on racemic CQ with no studies exploring the effect of the (R) and (S) enantiomers, which might potentially have additional benefits in other diseases. Additionally, evaluating other similarly acting antimalarials in clinical use and structural analogs could help maximize the intrinsic value of the 4-aminoquinolines. With regard to cancer therapy, successful repurposing of CQ-containing compounds will require linking the mode of action of these antimalarials with the signaling pathways that drive cancer cell proliferation to facilitate the development of a 4-amino-7-chloroquinoline that can be used as a synergistic partner in anticancer combination chemotherapy.     

Safety profile of new anticancer drugs

Importance of the field: The development of targeted anticancer therapies stems from advances in molecular biology. New agents range from antibodies that form complexes with antigens on the surface of the cancer cell to small molecules that have been engineered to block key enzymatic reactions. The interaction of the antibody or drug with its target inhibits key pathways involved in cell proliferation or metastasis, or activates pathways leading to cell death. Such pathways constitute ideal pharmacological targets. Clinical benefits from these novel therapeutic strategies are striking for patients with metastatic diseases.

Areas covered: This review analyses the main toxicities among most common targeted therapies that have been approved by the FDA or European Medicines Agency for their clinical utilisation in solid tumours treatment.

What the reader will gain: Here, the main toxicity and safety data among new anticancer targeted therapies are described. Data are organised through the pathways targeted by the drugs.

Take home message: The emergence of new targeted anticancer therapies promises more efficient and less toxic therapies. Generally, they are well tolerated, toxicities are commonly mild to moderate and can be handled rapidly. However, if most of these adverse events are manageable, life threatening and fatal complications can still occur.     

Vasopressin V1a and V1b receptor modulators: a patent review (2012 – 2014)

Introduction: The vasopressin V1a and V1b receptors are involved in many crucial physiological, reproductive, behavioral and social functions. Consequently, they are also involved in several pathological conditions, thus the ligands capable of selective stimulation/inhibition of these receptors may present therapeutic benefit in a variety of diseases.

Areas covered: In this review, the author focuses on the vasopressin V1a and V1b receptors, their biological functions and agonists and antagonists patented in the years 2012 – 2014. This paper is divided according to both the target receptor and the applicant and describes the compounds from the patents along with their biological activity.

Expert opinion: In the recent years, pharmaceutical companies have discovered and patented new compounds which act through vasopressin V1a and/or V1b receptors, both peptide and non-peptide. Among the V1bR antagonists published in the last years, the oxindole derivatives appear to be the most promising drug candidates.     

Therapeutic potential of boswellic acids: a patent review (1990-2015)

Introduction: Boswellic acids (BAs), a group of pentacyclic triterpenoids, have demonstrated very interesting biological properties that resulted in a number of protocols being developed for their synthesis. During the last twenty-five years (1990–2015), numerous BAs have been prepared. Both natural BAs and their synthetic derivatives can be used to treat various cancers as well as inflammatory diseases.

Areas covered: This review covers patents on therapeutic activities of natural BAs and their synthetic derivatives published in last twenty-five years (1990–2015). Only BA patents to treat cancer and inflammation are available. A discussion about structure-activity relationships (SAR) of these analogs is also included.

Expert opinion: BAs possess excellent anticancer and anti-inflammatory properties. A large number of BAs and their analogues have been prepared through modification at the C₃-OH and C₂₄-CO₂H functional groups. Most importantly, the C-24 amide and amino derivatives demonstrated increased anticancer and anti-inflammatory activity compared with other BA derivatives. Furthermore, BAs have the potential to form conjugates with other anticancer drugs that will synergistically enhance their anticancer effects; and we believe that in order to get lead compounds, there needs to be a greater focus on the synthesis of halo derivatives of BAs.     

Podophyllotoxin derivatives: a patent review (2012 – 2014)

Introduction: Podophyllotoxin (PPT) is a naturally occurring antimitotic agent and an interesting lead in the development of anticancer agents. Its optimization led to the development of etoposide and teniposide used in combination chemotherapy with other anticancer drugs; unlike PPT these drugs act by inhibiting topoisomerases. Clinical success and toxicity issues at later stages of etoposide usage inclined researchers to develop structurally modified PPT derivatives. Some of the compounds obtained are under clinical investigations and are anticipated to reach the market.

Areas covered: The present review summarizes the attempts made by researchers across the globe to find out newer anticancer agents based on the PPT structure. It brings out the outline of the inventions filed in the form of patents during the years 2012 – 2014.

Expert opinion: After the successful development of etoposide and teniposide there has been considerable interest in the PPT skeleton to develop newer chemotherapeutic agents. In this regard, several PPT derivatives such as TOP53, GL331, NK611, F11782, and so on, have been developed and are undergoing clinical trials. However, its low natural abundance is a major problem in carrying out research on PPT skeleton. This issue is expected to be addressed with the development of newer synthetic strategies to access structurally modified PPTs.     

Lapachol and lapachone analogs: a journey of two decades of patent research(1997-2016)

Introduction: Lapachol (1), β-lapachone (2) and α-lapachone (3) are three well-studied natural products isolated from Tabebuia impetiginosa having most interesting chemodiversity and demonstrating diverse biological effects.

Areas covered: The current review summarizes the recent and past discovery of chemotherapeutic agents based on the compounds 1–3. This review presents an overview of patents filed over the past two decades (1997 to 2016) mostly relating to the anticancer effects of these lapachol and lapachone analogues.

Expert opinion: The large number of interesting patents published on the therapeutic potential of quinones 1–3 and their synthetic derivatives lends credence to the importance of these molecules. Moreover, these quinones demonstrated potent anticancer effects towards various cancer cell lines and chemical modification of these quinones have led to products displaying enhanced anticancer effects. It is noteworthy that the majority of patents published are on the anticancer effects of quinones 1–3 and their synthetic derivatives along with a limited number of additional biological effects. It is our opinion that in order to get lead compounds, there needs to be a greater focus on the elucidation of the precise mechanism of action of these compounds including SAR and in vivo studies.     

Nanoparticles as delivery carriers for anticancer prodrugs

Introduction: Prodrugs are inactive compounds which are metabolized in the body to produce parent active agents. It has been shown that prodrugs hold some advantages over conventional drugs, such as increased solubility, improved permeability and bioavailability, reduced adverse effects and prolonged half-lives. Optimization of the vehicles used is very important in order to employ the advantages of prodrugs. Nanocarriers are currently being widely used as prodrug vehicles because of their ability to enhance storage stability, modulate prodrug release and tumor-targeted delivery and protect against enzymatic attack. This combined approach of prodrugs and nanoparticles has a particular attraction for developing anticancer therapies.

Areas covered: This paper discusses liposomes, polymeric nanoparticles and lipid nanoparticles, which are all carriers commonly used for prodrug encapsulation. Macromolecular prodrugs can spontaneously form self-assembled nanoparticles with no intervention of other additives. This review also describes recent developments in prodrug delivery using nanoparticulate strategies. Pharmacokinetic, pharmacodynamic and cytotoxicity evaluations of anticancer prodrugs are systematically elucidated in this review.

Expert opinion: More profiles involved in animal and clinical studies will encourage the future applicability of prodrug nanocarrier therapy. The possible toxicity associated with nanoparticles is a concern for development of prodrug delivery.     

Acridine derivatives: a patent review (2009 – 2010)

Introduction: Acridines are highly important heterocyclic compounds with immense biological significance as they act as the central core of antitumor, anti-protozoan, antiviral and multi-drug resistance modulating agents. The tricyclic aromatic structure of acridine is primarily responsible for its intercalation with DNA by controlling its biological profile and the substitution pattern of the molecule, which leads to several other applications.

Areas covered: In this review, acridine-based functional molecules and patents of acridine derivatives filed from 2009 to 2010 are discussed. The latest information about the medical importance of new acridine-based molecules is also discussed (e.g., materials with sensing and electrical/thermal properties).

Expert opinion: The tricyclic aromatic heterocyclic structure of acridine has a lot of potential for biological and material utilization. The versatility of fluorescent acridines could be further enhanced by introducing amino-acid chains or other polar substituents on the central moiety, which due to increased water solubility could increase their effectiveness under physiological conditions.     

Rhodanine as a scaffold in drug discovery: a critical review of its biological activities and mechanisms of target modulation

Introduction: Rhodanine-based compounds have been associated with numerous biological activities. After many years of research in drug discovery, they have gained a reputation as being pan assay interference compounds (PAINS) and frequent hitters in screening campaigns. Rhodanine-based compounds are also aggregators that can non-specifically interact with target proteins as well as Michael acceptors and interfere photometrically in biological assays due to their color.

Areas covered: The authors review the recently reported biological activities of rhodanine-based compounds. Furthermore, the article provides details of their synthesis and occurrence in compound libraries through high-throughput screening (HTS) and virtual high-throughput screening (VHTS). Additionally, the authors provide the reader with possible mechanisms of non-specific target modulation, analysis of the crystal structures of enzyme–rhodanine complexes and a comparison of rhodanine and thiazolidine-2,4-dione moieties.

Expert opinion: The biological activity of compounds possessing a rhodanine moiety should be considered very critically despite the convincing data obtained in biological assays. In addition to the lack of selectivity, unusual structure–activity relationship profiles and safety and specificity problems mean that rhodanines are generally not optimizable.