6-Chloropurines and organostannanes in palladium catalyzed cross coupling reactions

Synthesis of Main Chain Purine-Based Copolymers and Effects of Monomer Design on Thermal and Optical Properties

The ability to incorporate diverse monomeric building blocks enables the development of advanced polymeric materials possessing a wide range of properties that suits them for myriad applications. Herein, that synthetic toolbox is expanded through the first report of purine-based copolymers in which purines are incorporated directly into the polymer main chain. Stille cross-coupling of dibromopurine monomers with benzodithiophene (BDT) comonomers is used to generate these "poly(purine)s", and variations in the substitution pattern of the purine monomer and BDT side-chains provides insight into the role of monomer design on their resultant thermal and photophysical properties. Specifically, thermal analyses show that poly(purine)s exhibit high thermal stability and high glass transition temperatures depending on the BDT side-chain substituents and substitution pattern of the purine-derived comonomer. Furthermore, optical properties measured via UV-vis and fluorescence spectroscopies show dependence on monomer substitution pattern. These findings demonstrate the viability of synthesizing poly(purine)s via metal-catalyzed cross-coupling reactions and highlight the potential to tailor poly(purine) properties via simple alterations of comonomers.

Microwave promoted C6-alkylation of purines through S(N)Ar-based reaction of 6-chloropurines with 3-alkyl-acetylacetone

C6-Alkylated purine analogues were obtained in good to excellent isolated yields by S(N)Ar reaction of 6-chloropurine derivatives with 3-alkyl-acetylacetone. 3-Alkyl-acetylacetones were employed as alkylating agents and C6-alkylated purines were obtained highly selectively within short reaction time under microwave irradiation conditions. This work is complementary to the classical coupling reactions for the synthesis of C6-alkylated purine analogues.

Reductive Dimerization of 2- and 6-Iodopurines: Side Reaction in Pd-Catalyzed Cross-Coupling of Iodopurines

In the presence of a Pd catalyst and a base, 6- and 2-iodopurine derivatives undergo reductive C-C dimerization with the formation of the corresponding 6,6'- or 2,2'-dimers. The best results of the dimerization were obtained in the presence of i-Pr2NEt as a base in DMF. Phosphine-free catalysts as well as catalysts containing phosphines can be used. In the presence of catalytic systems containing PPh3 the dimerization does not proceed. This dimerization may become an important side reaction in the Stille or the Suzuki-Miyaura reactions of iodopurines.

2,6-disubstituted and 2,6,8-trisubstituted purines as adenosine receptor antagonists

Purines have long been exploited as adenosine receptor antagonists. The substitution pattern about the purine ring has been well investigated, and certain criteria have become almost a prerequisite for good affinity at the adenosine A(1) receptor. The adaptation of the pharmacophore and the initial series of pyrimidines developed in an earlier publication resulted in a series of purines with an entirely new substitution pattern. One compound in particular, 8-cyclopentyl-2,6-diphenylpurine (31, LUF 5962) has been shown to be very promising with an affinity of 0.29 nM at the human adenosine A(1) receptor.

Cytotoxic activity of 6-alkynyl- and 6-alkenylpurines

6-Alkynyl- and 6-alkenylpurines have been screened for cytotoxic activity against a human chronic myelogenous leukemia cell line; K-562 cells using a [(3)H]-thymidine incorporation assay. Most alkynes displayed cytotoxicity comparable to, or better than, the known anticancer drugs 6-mercaptopurine and fludarabine. The 6-alkenylpurines, which are promising plant growth stimulators and 15-lipoxygenase inhibitors, exhibited only low toxicity.

[Creation of functional recognition molecules for chemical modification of gene expression]

Artificial molecules that exhibit specific recognition of duplex DNA have attracted great interest because of their potential application in the manipulation of gene expression. Specific chemical reactions to the target base within the predetermined site would secure selective inhibition at either translation or transcription reactions. A more interesting application would be to alter the reacted base structure to induce a point mutation. In our study, we have focused our efforts on: 1) development of new cross-linking molecules with high efficiency as well as high selectivity; 2) establishment of a new molecular basis for the formation of nonnatural triplexes; and 3) synthetic approaches to the new minor groove binders. This paper summarizes our recent results using two new functional molecules: 2-amino-6-vinylpurine derivatives as new cross-linking agents; and W-shaped nucleic acid analogues as new recognition molecules for the formation of nonnatural-type triplexes.

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.

Convenient syntheses of 6-methylpurine and related nucleosides

Efficient methods for the synthesis of 6-methylpurine (3), 9-(2-deoxy-beta-D-erythro-pentofuranosyl)-6-methylpurine (8), and 6-methyl-9-beta-D-ribofuranosylpurine (5) are described. Methodology involving the (Ph3P)4Pd catalyzed cross-coupling reaction of CH3ZnBr with several different 6-chloropurine derivatives is described in high yield. This methodology now provides a facile and high-yielding synthesis of 8, which is needed in significant amounts for studies in cancer gene therapy.

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.

N1-Substituted Hypoxanthine Derivatives from the Reaction of 6-Halopurines with Michael Acceptors Under the Conditions of Heck Reaction

The reaction of 6-iodo-, 9-benzyl-6-chloropurine and 7-benzyl-6-chloropurine with butyl acrylate, acrylonitrile, methyl vinyl ketone or methyl methacrylate under conditions of the Heck reaction in the presence of TlOAc or AgOAc afforded N1-alkylhypoxanthine derivatives. Formation of these unexpected products can be rationalised as a Tl+- or Ag+-assisted substitution of halogen with acetate anion. The 6-acetoxypurine derivative thus formed then eliminates ketene and gives 7-benzyl- or 9-benzylhypoxanthine. Conjugate addition of these compounds onto Michael acceptors furnishes the N1-substituted hypoxanthine derivatives.

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.