Functionalization of pyrrolo[2,3-d]pyrimidine by palladium-catalyzed cross-coupling reactions (review)

Directed Lithiation of Protected 4-Chloropyrrolopyrimidine: Addition to Aldehydes and Ketones Aided by Bis(2-dimethylaminoethyl)ether

Pyrrolopyrimidines are important scaffolds for the preparation of bioactive molecules. Therefore, developing efficient and flexible ways for selective functionalization of the pyrrolopyrimidine skeleton is of interest. We have investigated lithiation-addition at C-6 of protected 4-chloro-7H-pyrrolo [2,3-d]pyrimidine as a route to new building blocks for medicinal chemistry. It was found that bis(2-dimethylaminoethyl) ether as an additive increased the yield in the additional reaction with benzaldehyde. Deuterium oxide quench experiments showed that this additive offered both a higher degree of lithiation and increased stability of the lithiated intermediate. The substrate scope of the protocol was investigated with 16 aldehydes and ketones, revealing the method to be excellently suited for reaction with aldehydes, cyclohexanone derivatives and 2,2,2-trifluoroacetophenone, while being less efficient for acetophenones. Yields in the range of 46-93% were obtained.

First Total Synthesis of 5'-O-α-d-Glucopyranosyl Tubercidin

The first total synthesis of 5'-O-α-d-glucopyranosyl tubercidin was successfully developed. It is a structurally unique disaccharide 7-deazapurine nucleoside exhibiting fungicidal activity, and was isolated from blue-green algae. The total synthesis was accomplished in eight steps with 27% overall yield from commercially available 1-O-acetyl-2,3,5-tri-O-benzoyl-β-d-ribose. The key step involves stereoselective α-O-glycosylation of the corresponding 7-bromo-6-chloro-2',3'-O-isopropylidene-β-d-tubercidin with 2,3,4,6-tetra-O-benzyl-glucopyranosyl trichloroacetimidate. All spectra are in accordance with the reported data for natural 5'-O-α-d-glucopyranosyl tubercidin. Meanwhile, 5'-O-β-d-glucopyranosyl tubercidin was also prepared using the same strategy.

Carbodiimide-based synthesis of N-heterocycles: moving from two classical reactive sites to chemical bond breaking/forming reaction

Carbodiimides are a unique class of heterocumulene compounds that display distinctive chemical properties. The rich chemistry of carbodiimides has drawn increasing attention from chemists in recent years and has made them exceedingly useful compounds in modern organic chemistry, especially in the synthesis of N-heterocycles. This review has outlined the extensive application of carbodiimides in the synthesis of N-heterocycles from the 1980s to today. A wide range of reactions for the synthesis of various types of N-heterocyclic systems (three-, four-, five-, six-, seven-, larger-membered and fused heterocycles) have been developed on the basis of carbodiimides and their derivatives.

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

The synthesis of novel fluorescent N(9)-alkylated 2-amino-6-triazolylpurine and 7-deazapurine derivatives is described. A new C(2)-regioselectivity in the nucleophilic aromatic substitution reactions of 9-alkylated-2,6-diazidopurines and 7-deazapurines with secondary amines has been disclosed. The obtained intermediates, 9-alkylated-2-amino-6-azido-(7-deaza)purines, were transformed into the title compounds by CuAAC reaction. The designed compounds belong to the push-pull systems and possess promising fluorescence properties with quantum yields in the range from 28% to 60% in acetonitrile solution. Due to electron-withdrawing properties of purine and 7-deazapurine heterocycles, which were additionally extended by triazole moieties, the compounds with electron-donating groups showed intramolecular charge transfer character (ICT/TICT) of the excited states which was proved by solvatochromic dynamics and supported by DFT calculations. In the 7-deazapurine series this led to increased fluorescence quantum yield (74%) in THF solution. The compounds exhibit low cytotoxicity and as such are useful for the cell labelling studies in the future.

C-H Imidation of 7-Deazapurines

We developed and presented here a ferrocene-catalyzed C-H imidation of 7-deazapurines (pyrrolo[2,3-d]pyrimidines) with N-imidyl peroxyesters. The reactions occur regioselectively at position 8 in 7-deazapurines, leading to a series of 8-succinimido-, phtalimido-, or naphthalimido-7-deazapurine derivatives. Attempted hydrazinolysis of resulting 8-imidyl-7-deazapurines led to corresponding 8-amino-7-deazapurine, which was very unstable and quickly decomposed.

Regioselective C–H and N–H functionalization of purine derivatives and analogues: a synthetic and mechanistic perspective

This perspective provides a systematic and concise overview of the recent development in C–H/N–H bond functionalization in purine derivatives and analogues.

Synthesis and Cytostatic and Antiviral Profiling of Thieno-Fused 7-Deazapurine Ribonucleosides

Two isomeric series of new thieno-fused 7-deazapurine ribonucleosides (derived from 4-substituted thieno[2',3':4,5]pyrrolo[2,3-d]pyrimidines and thieno[3',2':4,5]pyrrolo[2,3-d]pyrimidines) were synthesized by a sequence involving Negishi coupling of 4,6-dichloropyrimidine with iodothiophenes, nucleophilic azidation, and cyclization of tetrazolopyrimidines, followed by glycosylation and cross-couplings or nucleophilic substitutions at position 4. Most nucleosides (from both isomeric series) exerted low micromolar or submicromolar in vitro cytostatic activities against a broad panel of cancer and leukemia cell lines and some antiviral activity against HCV. The most active were the 6-methoxy, 6-methylsulfanyl, and 6-methyl derivatives, which were highly active to cancer cells and less toxic or nontoxic to fibroblasts.

Synthesis of 8-(1,2,3-triazol-1-yl)-7-deazapurine nucleosides by azide-alkyne click reactions and direct C-H bond functionalization

Treatment of toyocamycin or sangivamycin with 1,3-dibromo-5,5-dimethylhydantoin in MeOH (r.t./30 min) gave 8-bromotoyocamycin and 8-bromosangivamycin in good yields. Nucleophilic aromatic substitution of 8-bromotoyocamycin with sodium azide provided novel 8-azidotoyocamycin. Strain promoted click reactions of the latter with cyclooctynes resulted in the formation of the 1,2,3-triazole products. Iodine-mediated direct C8-H bond functionalization of tubercidin with benzotriazoles in the presence of tert-butyl hydroperoxide gave the corresponding 8-benzotriazolyltubercidin derivatives. The 8-(1,2,3-triazol-1-yl)-7-deazapurine derivatives showed moderate quantum yields and a large Stokes shifts of ~ 100 nm.

Synthesis and cytostatic activity of 7-arylsulfanyl-7-deazapurine bases and ribonucleosides

A series of novel 6-substituted 7-arylsulfanyl-7-deazapurine bases and nucleosides has been prepared for screening of anticancer activity. 7-Thienylsulfanyl-7-deazapurine bases exerted micromolar cytostatic affects.

Access to 6-arylpyrrolo[2,3-d]pyrimidines via a palladium-catalyzed direct C–H arylation reaction

A route to 6-arylpyrrolo[2,3-d]pyrimidines via a direct palladium-catalyzed C–H arylation reaction.

Direct C–H amination and C–H chloroamination of 7-deazapurines

Selective methods for Pd and Cu-catalyzed C–H aminations and chloroaminations of 7-deazapurines were developed.