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  Huabin Zhang,Shaowu Du CrystEngComm, 2014,16, 4059-4068

4-Chloro-8-fluoro-5H-pyrimido[5,4-b]indole (CAS No. 331443-96-0): A Promising Compound in Chemical Biology and Drug Development

The compound 4-Chloro-8-fluoro-5H-pyrimido[5,4-b]indole, identified by CAS Registry Number 331443-96-0, represents a structurally unique member of the pyrimido-indole class of heterocyclic compounds. Its molecular architecture combines the pharmacophoric potential of a pyrimidine ring fused to an indole system, with strategic halogen substitutions at positions 4 (chlorine) and 8 (fluorine). This configuration positions it as a compelling scaffold for exploring bioactivity modulation through rational design principles.

The pyrimido[5,4-b]indole core is recognized for its ability to engage protein targets via π-stacking interactions and hydrogen bonding networks. Recent advancements in computational chemistry have revealed that the chloro-substituted position 4 enhances hydrophobic interactions while the fluoro group at position 8 introduces electronic perturbations that stabilize specific binding orientations. These structural features were highlighted in a 2022 study published in *Chemical Science*, where analogous compounds demonstrated selective inhibition of kinases involved in cancer cell proliferation.

Synthetic strategies for accessing this compound have evolved significantly since its initial synthesis reported by the Smith group in 2019. Modern protocols now employ microwave-assisted condensation of indole derivatives with β-ketoesters under solvent-free conditions, achieving >90% yield within 1 hour. This methodological refinement has enabled scalable production for preclinical evaluation, as evidenced by ongoing investigations into its antiviral properties against RNA-dependent RNA polymerases.

In vitro assays conducted by Li et al. (Nature Communications, 2023) demonstrated that CAS No. 331443-96-0-based analogs exhibit submicromolar IC?? values against SARS-CoV-2 protease activity without significant cytotoxicity to Vero E6 cells at therapeutic concentrations. The fluorine atom's ability to mimic phosphate groups was proposed as a key factor in enzyme pocket recognition, suggesting potential utility in pandemic response strategies.

Beyond virology applications, this compound's structural versatility has been leveraged to create multitarget ligands addressing neurodegenerative pathways. A collaborative study between MIT and Genentech (ACS Medicinal Chemistry Letters, 2023) showed that fluorine-modified pyrimido-indoles can simultaneously inhibit both β-secretase and tau phosphorylation processes associated with Alzheimer's disease progression. The chlorine substitution was found critical for blood-brain barrier permeability optimization.

Ongoing mechanistic studies using cryo-electron microscopy have revealed unprecedented binding modes where the indole nitrogen forms hydrogen bonds with enzyme catalytic residues while the pyrimidine ring engages aromatic stacking interactions with adjacent helices. This dual interaction mechanism explains its enhanced selectivity compared to earlier generation inhibitors lacking these halogenated substituents.

In drug delivery contexts, researchers at ETH Zurich have developed nanoparticle formulations incorporating this compound's derivatives with pH-sensitive release profiles (Advanced Materials, 2023). The chlorine's electron-withdrawing effect was exploited to stabilize drug payloads until reaching acidic tumor microenvironments, demonstrating up to 7-fold increase in therapeutic index compared to free drug administration.

Clinical translation efforts are currently focused on optimizing metabolic stability through bioisosteric replacements while maintaining key pharmacophore elements. Phase I trials targeting chronic myeloid leukemia are anticipated by Q1 2025 following promising results from xenograft models showing tumor growth inhibition exceeding imatinib controls without myelosuppression side effects.

This compound's structural characteristics align with modern drug design paradigms emphasizing ligand efficiency and target selectivity. Its ability to modulate multiple biological processes through subtle structural variations underscores its value as a lead molecule for developing next-generation therapeutics across oncology, virology, and neurology indications.

• 107400-97-5(4-Chloro-5H-pyrimido5,4-bindole HCl)
• 16499-62-0(4-Chloro-7-fluoroquinazoline)
• 331443-97-1(4-Chloro-8-methyl-5H-pyrimido5,4-bindole)
• 98792-02-0(4-chloro-5H-pyrimido5,4-bindole)
• 549488-69-9(4,8-Dichloro-5H-pyrimido[5,4-b]indole)
• 16499-61-9(4-chloro-6-fluoro-quinazoline)
• 1263285-23-9(4-chloro-5h-pyrido[4',3':4,5]pyrrolo[3,2-d]pyrimidine)
• 84905-80-6(4-Chloro-5H-pyrrolo[3,2-d]pyrimidine)
• 1311275-30-5(4-Chloro-7-fluoro-5H-pyrrolo[3,2-d]pyrimidine)
• 1379307-68-2(2,4-Dichloro-7-fluoro-5H-pyrrolo[3,2-d]pyrimidine)