Design and racemic synthesis of conformationally restricted carbocyclic pyrimidine nucleoside analogs based on the structure of the L-nucleoside residue in heterochiral DNA

Exploring the role of chirality in nucleic acid recognition

The study of the base-pairing properties of nucleic acids with sugar moieties in the backbone belonging to the L-series (β-L-DNA, β-L-RNA, and their analogs) are reviewed. The major structural factors underlying the formation of stable heterochiral complexes obtained by incorporation of modified nucleotides into natural duplexes, or by hybridization between homochiral strands of opposite sense of chirality are highlighted. In addition, the perspective use of L-nucleic acids as candidates for various therapeutic applications, or as tools for both synthetic biology and etiology-oriented investigations on the structure and stereochemistry of natural nucleic acids is discussed.

A linchpin carbacyclization approach for the synthesis of carbanucleosides

A convenient synthesis of carbanucleosides, with both enantiomers equally accessible, is reported. The key step is a tandem linchpin cyclization process to give access to substituted carbafuranose derivatives having the correct relative stereochemistry for subsequent nucleobase introduction with inversion of configuration at C1. This was illustrated by the synthesis of 2',3'-dideoxycarbathymidine via a convergent nucleobase introduction and of 2',3'-dideoxy-6'-hydroxycarbauridine via a linear nucleobase introduction. Both methods relied on Mitsunobu chemistry, and the first example of the Mukaiyama modification of the Mitsunobu reaction involving nucleobases as nucleophiles is reported.

Efficient synthesis of bicyclic oxazolino- and thiazolino[3,2-c]pyrimidine-5,7-diones and its application to the synthesis of GnRH antagonists

Treatment of various 2-methyl oxazolines or thiazolines with chlorocarbonyl isocyanate gives the corresponding bicyclic oxazolino- or thiazolino[3,2-c]pyrimidin-5,7-dione derivatives in very good yield. This reaction has been applied to the rapid syntheses of human gonadotropin-releasing hormone (hGnRH) receptor antagonists for SAR study, resulting in 13e with binding affinity in the low nanomolar range (4.5 nM).

Synthesis and hybridization properties of l-oligodeoxynucleotide analogues fixed in a low anti glycosyl conformation

We have synthesized l-type enantiomers (cU and cA) of nucleoside analogues, whose glycosyl bonds are fixed in a low anti conformation (ap glycosyl conformation, [small chi][approximate] 180[degree]), and incorporated them into oligonucleotides to evaluate the hybridization ability with natural DNA and RNA sequences. Although the incorporation of the modified nucleosides into oligonucleotides decreased the hybridization ability with unmodified complementary DNA sequences, the fully-substituted 12mers (cU(12) and cA(12)) still retained the hybridization ability with the complementary unmodified DNA 12mers, regardless of their unnatural l-chirality. In contrast, cU(12) and cA(12) showed different hybridization behavior with complementary unmodified RNA 12mers. cU(12) forms a more stable duplex with rA(12) than the corresponding natural 12mer (dT(12)), whereas cA(12) cannot hybridize with rU(12). Based on the model structure of cU(12)-rA(12), we discuss these experimental results.