Soheila Azim Patrawala* 1
The past decade has witnessed the ascendancy of heterocycle synthesis as a pivotal domain within synthetic organic chemistry, driven by the diverse applications of these compounds in medicinal and pharmaceutical contexts. The utilization of heterocycles as privileged structures in drug discovery represents a central focus within medicinal chemistry. These privileged structures, characterized by their capacity to act as ligands for a spectrum of biological receptors with high binding affinities, offer a strategic approach for the expedited discovery of novel bioactive compounds across a broad spectrum of therapeutic areas. Consequently, contemporary research in heterocyclic chemistry emphasizes the synthesis of biheterocyclic architectures, including conjugated tri- or tetracyclic molecules incorporating multiple privileged structural motifs. [1-3]
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- CANCER
Cancer encompasses a diverse group of diseases characterized by dysregulated cellular proliferation and differentiation. This uncontrolled growth manifests as tumors, except in leukemias, where abnormal cell division disrupts blood function. Malignancy arises from cellular abnormalities, stemming from inherited genetic mutations or environmental exposures like chemicals, radiation, or infectious agents. Tumors can disrupt vital physiological systems, including digestive, nervous, and circulatory functions, and secrete hormones that alter bodily processes. Benign tumors exhibit localized growth, whereas malignant tumors invade surrounding tissues and metastasize through angiogenesis and lymphatic/hematogenous dissemination. Cancer treatment modalities include surgery, radiation, immunotherapy, chemotherapy, and chemoprevention. Ideally, anticancer drugs would selectively eradicate malignant cells without harming healthy tissues. However, current chemotherapeutic agents, often targeting DNA replication and transcription, exhibit significant toxicities, necessitating a careful assessment of the therapeutic index. Cellular growth and division are tightly regulated processes, governed by a balance between growth-promoting and growth-suppressing genes. Cancer emerges when these regulatory mechanisms are disrupted, leading to unchecked cell proliferation. Genetic mutations, arising from external factors or errors during cell division, can accumulate, enabling cells to evade normal control mechanisms and proliferate uncontrollably. The body possesses error-correction mechanisms, but cancer cells can circumvent these, fostering further genetic instability and tumor progression.
1.2 TARGET FOR ANTICANCER DRUGS
Contemporary oncology therapeutics frequently target cell surface receptors or intracellular phosphoproteins and kinases within key signaling pathways. Elucidating the phosphorylation status of pivotal signaling molecules in tumor cells provides crucial insights into the tumor's type, stage, and dynamic state. This information is paramount for accurate diagnosis, precise prognostication, and the formulation of personalized treatment strategies. [4,5]
1.2.1 Epidermal Growth Factor Receptor
The ErbB, or epidermal growth factor receptor (EGFR), family comprises four structurally related receptor tyrosine kinases. The nomenclature, ErbB, originates from its homology to the erythroblastic leukemia viral oncogene. Inadequate ErbB signaling in humans correlates with the pathogenesis of neurodegenerative disorders, including multiple sclerosis and Alzheimer's disease. Conversely, in murine models, ablation of signaling from any ErbB family member results in embryonic lethality, accompanied by developmental defects in vital organs such as the lungs, skin, heart, and brain. Furthermore, aberrant ErbB signaling is implicated in the development of a broad spectrum of solid tumors. Notably, ErbB-1 and ErbB-2 are frequently overexpressed in human malignancies, and their amplified signaling pathways are considered critical drivers of tumorigenesis and malignant progression.
Structure of EGFR
The epidermal growth factor receptor belongs to the ErbB family of receptor tyrocine kinases (RTK). There are four members of the EGFR family20:
a) ErbB-1, also named epidermal growth factor receptor (EGFR)
b) ErbB-2, also named HER2 in humans and in rodents
c) ErbB-3, also named HER3
d) ErbB-4, also named HER4
e) V-ErbBs are homologous to EGFR, but lack sequences within the ligand binding ectodomain.
The epidermal growth factor receptor is the cell-surface receptor for members of the epidermal growth factor family (EGF-family) of extracellular protein ligands composed of extracellular domain, a hydrophobic transmembrane domain and intracellular domain. [6,7]
Role of EGFR in Kinase Activation
The ErbB protein family, comprising four members, exhibits the capacity to form homo- and heterodimers, and potentially higher-order oligomers, upon activation by a subset of eleven distinct growth factor ligands. The ligand-receptor interaction specificity is characterized by differential activation capabilities, as delineated in the provided table. In the absence of ligand binding, ErbB-1, -3, and -4 adopt a 'tethered' conformation, wherein a 10-amino-acid dimerization arm is sterically hindered, precluding monomer-monomer interactions. Conversely, ligand binding to ErbB-1, or the intrinsic conformational state of unliganded ErbB-2, results in the untethering and exposure of the dimerization arm, facilitating receptor dimerization. Ectodomain dimerization engenders the spatial juxtaposition of cytoplasmic domains, enabling transphosphorylation of specific tyrosine, serine, and threonine residues within each ErbB subunit. For ErbB-1, at least ten tyrosine, seven serine, and two threonine phosphorylation sites have been identified, with some sites, such as Tyr 992, subject to dephosphorylation upon receptor dimerization. Despite the multiplicity of potential phosphorylation sites, typically only one, or rarely two, sites are phosphorylated concurrently following dimerization, indicating a tightly regulated phosphorylation cascade. [8-11]
Role of EGFR in Cancer
The receptor tyrosine kinases ErbB-1 (EGFR) and ErbB-2 (HER-2) are critical regulators of cellular proliferation and differentiation. Aberrant overexpression and/or hyperactivation of these receptors are frequently observed across diverse tumor types. EGFR plays a pivotal role in the pathogenesis and progression of various carcinomas, including those of the breast, lung, ovary, prostate, and head and neck. In human carcinomas, EGFR and its cognate EGF-like peptide ligands are often overexpressed, and both in vivo and in vitro studies have demonstrated their capacity to induce cellular transformation. Consequently, inhibitors targeting the EGFR protein tyrosine kinase (PTK) hold significant therapeutic promise for the treatment of both malignant and non-malignant epithelial disorders. [12-17]
Inhibitors of EGFR
The concept of targeting EGFR for cancer therapy emerged in the 1980s, yielding diverse therapeutic strategies. These include monoclonal antibodies (mAbs), such as cetuximab (Erbitux), which target the extracellular domain of EGFR, and small molecule tyrosine kinase inhibitors (TKIs), like gefitinib (Iressa) and erlotinib (Tarceva), that inhibit receptor signaling by targeting the catalytic kinase domain. Cetuximab, a chimeric mAb, has been extensively studied and clinically approved for specific EGFR inhibition. A complementary approach involves TKIs that disrupt EGFR tyrosine kinase (TK) domain activation. These agents competitively inhibit ATP binding to the TK domain, thereby selectively blocking EGFR autophosphorylation. TKIs are synthetic, predominantly quinazoline-derived, low-molecular-weight compounds that interact with the intracellular TK domain of EGFR and other receptors. They impede ligand-induced receptor phosphorylation through competitive bidding at the intracellular Mg-ATP-binding site. [18-22]
1.3 Quinazoline
The interest in this heterocycle prompted us to set up a short and efficient route toward quinazoline nucleus. The quinazoline nucleus is a very attractive and useful scaffold in medicinal chemistry: it can be found as a pharmacophore in a wide variety of biologically active compounds, such as antitumorals, antibacterials, antivirals, and many other therapeutic agents. The name quinazoline (1) was first proposed for this compound by Weddige, on observing that this was isomeric with the compounds cinnoline (2) and quinoxaline (3). Paal and Bush 34 suggested the numbering of quinazoline ring system, which is currentlyused. The other less commonly used na,es for this ring system are ‘phenmiazine’ and 5,6-benzopyrimidine. However, the name quinazoline is now universally accepted.
There are many derivatives of quinazoline system known so far, among which keto- quinazolines also called as quinazolinones, are the most important compounds. Depending upon the position of the keto or oxo group, these compounds may be classified inti two types: 2-(1H) quinazolinones or 1,2dihydro-2-oxoquinazolines and 4(3H)-quinazolines or 3,4-dihydro-oxoquinazolines. These systems exhibit lactam- lactim tautomerism and undergo hydroxyl group replacement reactions. 2-Cyano- 4(3H)-quinazolinone was the first quinazolinone derivative to be synthesized. [23,24]
1.4 Benzothiazole:
10.5281/zenodo.15212322