Synthesis and cytostatic activity of nucleosides and acyclic nucleoside analogues derived from 6-(trifluoromethyl)purines

Recent Advances in the Synthesis of Acyclic Nucleosides and Their Therapeutic Applications

DNA is commonly known as the "molecule of life" because it holds the genetic instructions for all living organisms on Earth. The utilization of modified nucleosides holds the potential to transform the management of a wide range of human illnesses. Modified nucleosides and their role directly led to the 2023 Nobel prize. Acyclic nucleosides, due to their distinctive physiochemical and biological characteristics, rank among the most adaptable modified nucleosides in the field of medicinal chemistry. Acyclic nucleosides are more resistant to chemical and biological deterioration, and their adaptable acyclic structure makes it possible for them to interact with various enzymes. A phosphonate group, which is linked via an aliphatic functionality to a purine or a pyrimidine base, distinguishes acyclic nucleoside phosphonates (ANPs) from other nucleotide analogs. Acyclic nucleosides and their derivatives have demonstrated various biological activities such as anti-viral, anti-bacterial, anti-cancer, anti-microbial, etc. Ganciclovir, Famciclovir, and Penciclovir are the acyclic nucleoside-based drugs approved by FDA for the treatment of various diseases. Thus, acyclic nucleosides are extremely useful for generating a variety of unique bioactive chemicals. Their biological activities as well as selectivity is significantly influenced by the stereochemistry of the acyclic nucleosides because chiral acyclic nucleosides have drawn a lot of interest due to their intriguing biological functions and potential as medicines. For example, tenofovir's (R) enantiomer is roughly 50 times more potent against HIV than its (S) counterpart. We can confidently state, "The most promising developments are yet to come in the realm of acyclic nucleosides!" Herein, we have covered the most current developments in the field of chemical synthesis and therapeutic applications of acyclic nucleosides based upon our continued interest and activity in this field since mid-1990's.

Design, Synthesis, and Activity Evaluation of Novel Acyclic Nucleosides as Potential Anticancer Agents In Vitro and In Vivo

In the present work, 103 novel acyclic nucleosides were designed, synthesized, and evaluated for their anticancer activities in vitro and in vivo. The structure-activity relationship (SAR) studies revealed that most target compounds inhibited the growth of colon cancer cells in vitro, of which 3-(6-chloro-9H-purin-9-yl)dodecan-1-ol (9b) exhibited the most potent effect against the HCT-116 and SW480 cells with IC50 values of 0.89 and 1.15 μM, respectively. Furthermore, all of the (R)-configured acyclic nucleoside derivatives displayed more potent anticancer activity compared to their (S)-counterparts. Mechanistic studies revealed that compound 9b triggered apoptosis in the cancer cell lines via depolarization of the mitochondrial membrane and effectively inhibited colony formation. Importantly, compound 9b inhibited the growth of the SW480 xenograft in a mouse model with low systemic toxicity. These results indicated that acyclic nucleoside compounds are viable as potent and effective anticancer agents, and compound 9b may serve as a promising lead compound that merits further attention in future anticancer drug discovery.

A comparative study on FT-IR, conformational and electronic structure of 6-methylpurine

In this work, the experimental and theoretical study on molecular structure and vibrational spectra of 6-methylpurine were studied. A detailed quantum chemical calculations have been performed by Hartree-Fock (HF) and density functional theory (DFT) methods (B3LYP) with 6-31++G(d,p) basis sets. Ultraviolet-visible (UV-Vis) spectra, thermodynamic properties and Natural Bond Orbital (NBO) analysis of the title compound in the ground state have been calculated using the Hartree-Fock (HF) and density functional theory (DFT) methods (B3LYP) with 6-31++G(d,p) basis set combination for the first time. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results show that the vibrational frequencies are in good agreement with the experimental data. In addition, not only were frontier molecular orbitals (HOMO and LUMO), molecular electrostatic potential (MEP) and density of the state (DOS) energy band gap values were predicted.

Efficient synthesis and biological properties of the 2′-trifluoromethyl analogues of acyclic nucleosides and acyclic nucleoside phosphonates

Efficient and optimized procedure for the preparation of several acyclic nucleosides and acyclic nucleoside phosphonates substituted at the C-2′ position of the aliphatic part by the trifluoromethyl group is described. Trifluoromethyloxirane was found to be an excellent reagent for the introduction of the 1,1,1-trifluoropropan-2-ol moiety. Surprisingly, the next reaction of these 1,1,1-trifluoropropan-2-ols with the reagent for the introduction of the methylphosphonic residue afforded the desired phosphonates in very high yields and finally a novel simple and scalable procedure for the isolation of free phosphonic acids, after the reaction of dialkyl phosphonates with bromotrimethylsilane, was developed. Prepared compounds were evaluated for their biological properties, but none of the prepared phosphonic acids or acyclic nucleosides exhibits any antiviral, antiproliferative or anti-toxin activities.

Palladium-catalyzed cross-coupling reactions in c6 modifications of purine nucleosides

This unit describes the cross-coupling methodology for introduction of diverse C-substituents to position 6 of purine nucleosides. Protected 6-chloropurine nucleosides undergo Pd-catalyzed cross-coupling reactions with trialkylaluminium, alkylzinc halides, aryl(tributyl)stannanes, and arylboronic acids to give the corresponding 6-substituted intermediates, which can be deprotected by treatment with NaOMe. (Acetyloxy)methylzinc iodide is used for introduction of the hydroxymethyl group, which can further be transformed to fluoromethyl and difluoromethyl groups. Most of the title 6-substituted purine ribonucleosides possess cytostatic and/or anti-HCV activity.

Cytostatic and antiviral 6-arylpurine ribonucleosides. Part 7: Synthesis and evaluation of 6-substituted purine l-ribonucleosides

A series of purine l-ribonucleosides 2a-2i bearing diverse C-substituents (alkyl, aryl, hetaryl or hydroxymethyl) in the position 6 were prepared by Pd-catalyzed cross-coupling reactions of 6-chloro-9-(2,3,5-tri-O-acetyl-beta-l-ribofuranosyl)purine with the corresponding organometallics followed by deprotection. Unlike their d-ribonucleoside enantiomers that possess strong cytostatic and anti-HCV activity, the l-ribonucleosides were inactive except for 6-benzylpurine nucleoside 2h showing moderate anti-HCV effect in replicon assay. A triphosphate of 2h did not inhibit HCV RNA polymerase.

Cytostatic and Antiviral 6-Arylpurine Ribonucleosides VIII. Synthesis and Evaluation of 6-Substituted Purine 3'-Deoxyribonucleosides

A series of purine 3'-deoxyribonucleosides bearing diverse C-substituents (alkyl, aryl, hetaryl or hydroxymethyl) in the position 6 was prepared by Pd-catalyzed cross-coupling reactions of 6-iodo-9-[2,5-bis-O-(tert-butyldimethylsilyl)-3-deoxy-β-D-ribofuranosyl]purine with the corresponding organometallics followed by deprotection by (HF)3·Et3N. None of the title 3'-deoxyribonucleoside showed any cytostatic activity or anti-HCV effect in replicon assay.

The first synthesis and cytostatic activity of novel 6-(fluoromethyl)purine bases and nucleosides

Two alternative approaches to the synthesis of novel 6-(fluoromethyl)purine bases and nucleosides are described either by direct deoxyfluorination or by multistep functional group transformations starting from 6-(hydroxymethyl)purines. 6-(fluoromethyl)purine ribonucleoside displayed significant cytostatic effects.

Synthesis of 1-Glycosyl Derivatives of Benzocamalexin

The linear synthesis of 1-(β-D-glucopyranosyl)-, 1-(β-D-galactopyranosyl)-, 1-(β-D-mannopyranosyl)- and 1-(β-D-ribofuranosyl)benzocamalexin was elaborated from indoline as a starting compound and corresponding pentaacetylhexoses or 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribose as suitable glycosyl donors.

Covalent analogues of DNA base-pairs and triplets. Part 2: synthesis and cytostatic activity of bis(purin-6-yl)acetylenes,-diacetylenes and related compounds

The title bis(purin-6-yl)acetylenes, -diacetylenes, -ethylenes and -ethanes were prepared as covalent base-pair analogues starting from 6-ethynylpurines and 6-iodopurines by cross-coupling and homo-coupling reactions and hydrogenations. The bis(purin-6-yl)acetylenes and -diacetylenes exhibited significant cytostatic activity in vitro (IC(50)=0.4-1.0 micromol/l).

Covalent Analogues of DNA Base-Pairs and Triplets V. Synthesis of Purine-Purine and Purine-Pyrimidine Conjugates Connected by Diverse Types of Acyclic Carbon Linkages

The title 1,2-bis(purin-6-yl)acetylenes, -diacetylenes, -ethylenes and -ethanes were prepared as covalent base-pair analogues starting from 6-ethynylpurines and 6-iodopurines by the Sonogashira cross-coupling or oxidative alkyne-dimerization reactions followed by hydrogenations. 6-[(1,3-Dimethyluracil-5-yl)ethynyl]purine (11) was prepared analogously and hydrogenated to the corresponding purine-pyrimidine conjugates linked via vinylene and ethylene linkers. Unlike the cytostatic bis(purin-6-yl)acetylenes and -diacetylenes, the purine-pyrimidine conjugates were inactive. Crystal structures of bis(purin-6-yl)acetylene 6a, -diacetylene 8a and -ethane 5a were determined by single-crystal X-ray diffraction.

Synthesis and analysis of RNA containing 6-trifluoromethylpurine ribonucleoside

We report the synthesis of a 5'-DMT-2'-TBDMS-protected phosphoramidite of 6-trifluoromethylpurine ribonucleoside ((TFM)P) and its use in the site-specific incorporation of 6-trifluoromethylpurine into RNA. Properties of (TFM)P-substituted RNA suggest it will be valuable in the study of RNA structure and the binding of RNA-modifying enzymes, particularly the RNA-editing adenosine deaminases. Reaction: see text.

Cytostatic 6-Arylpurine Nucleosides III. Synthesis and Structure-Activity Relationship Study in Cytostatic Activity of 6-Aryl-, 6-Hetaryl- and 6-Benzylpurine Ribonucleosides

A series of fifteen 6-aryl-, 6-hetaryl- and 6-benzylpurine ribonucleosides has been prepared by Pd-catalyzed cross-coupling reactions of 6-chloro-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)- purine with arylboronic acids, hetarylzinc halides, hetarylstannanes or benzylzinc halides followed by deprotection. Structure-activity relationship study revealed that besides 6-(4-substituted phenyl)purine nucleosides, also some 6-hetaryl- and 6-benzylpurine ribonucleosides possess considerable cytostatic activity.

Synthesis and cytostatic activity of substituted 6-phenylpurine bases and nucleosides: application of the Suzuki-Miyaura cross-coupling reactions of 6-chloropurine derivatives with phenylboronic acids

The Suzuki-Miyaura reaction of protected 6-chloropurine and 2-amino-6-chloropurine bases and nucleosides with substituted phenylboronic acids led to the corresponding protected 6-(substituted phenyl)purine derivatives 6-9. Their deprotection yielded a series of substituted 6-phenylpurine bases and nucleosides 10-13. Significant cytostatic activity (IC(50) 0.25-20 micromol/L) in CCRF-CEM, HeLa, and L1210 cell lines was found for several 6-(4-X-substituted phenyl)purine ribonucleosides 12 (X = H, F, Cl, and OR), while the 6-phenylpurine and 2-amino-6-phenylpurine bases 10 and 11, as well as 2-amino-6-phenylpurine ribosides 13, were entirely inactive against these cell lines.

Cytostatic 6-Arylpurine Nucleosides II. Synthesis of Sugar-Modified Derivatives: 9-(2-Deoxy-β-D-erythro-pentofuranosyl)-, 9-(5-Deoxy-β-D-ribofuranosyl)- and 9-(2,3-Dihydroxypropyl)-6-phenylpurines

9-(2-Deoxy-β-D-erythro-pentofuranosyl)-6-(4-substituted phenyl)purines, 9-(5-deoxy-β-D-ribofuranosyl)-6-(4-substituted phenyl)purines and 9-(2,3-dihydroxypropyl)-6-(4-substituted phenyl)purines were prepared by the Suzuki-Miyaura cross-coupling reactions of the corresponding protected 9-substituted 6-chloropurines with substituted phenylboronic acids followed by MeONa mediated deprotection. In contrast to the highly active 6-phenylpurine ribonucleosides, the title compounds did not show any considerable cytostatic activity.

Synthesis of Acyclic Nucleotide Analogues Derived from 2-Amino-6-C-substituted Purines via Cross-Coupling Reactions of 2-Amino-9-{2-[(diisopropoxyphosphoryl)methoxy]ethyl}-6-halopurines with Diverse Organometallic Reagents

Cross-coupling reactions of 2-amino-6-chloro-9-{2-[(diisopropoxyphosphoryl)methoxy]ethyl}purine (1) and 2-amino-9-{2-[(diisopropoxyphosphoryl)methoxy]ethyl}-6-iodopurine (2) with diverse types of organometallic reagents have been studied. Arylboronic acids reacted with 1 to give the corresponding 2-amino-6-arylpurines 3a-3d in good yields. Analogously, trialkylaluminium reagents were used for the preparation of 6-alkyl-2-aminopurines 3k and 3l from 1. Hetarylzinc halides and hetarylstannanes required the use of 2-amino-6-iodopurine 2 to give the corresponding 2-amino-6-hetarylpurines 3e-3j in fair to good yields. A CuI/KF mediated coupling of perfluoroalkylsilanes with 2 afforded the 2-amino-6-perfluoroalkylpurines 3m and 3n in moderate yields. Cleavage of the esters 3 with bromo(trimethyl)silane gave the target free phosphonates 4 that were purified by ion- exchange chromatography. The title compounds were tested on antiviral and cytostatic activity.