Synthesis of cyclopentane analogs of 1-(2′,3′-dideoxy-β-glycero-pentofuranosyl)pyrimidine nucleosides

Abstract

Synthesis of new carbocyclic analogs of 1-(2′,3′-dideoxy-glycero-pentofuranosyl)pyrimidine nucleosides having the uracil (34), 2-thiouracil (33), 2-thiothymine (31), cytosine (44), and 5-methylcytosine (43) bases is described. The nucleoside analogs having the uracil, 2-thiouracil, and 2-thiothymine bases were prepared by coupling cis-3-aminocyclopentanemethanol (8) with 3-ethoxypropenoyl isocyanate (26), 3-ethoxypropenoyl isothiocyanate (25), and 3-methoxy-2-methylpropenoyl isothiocyanate (23), respectively, to give the corresponding acyl urea (30) and acyl thioureas (29 and 27). The acyl urea was cyclized in 2 N H₂SO₄ and the acyl thioureas in 15 N aqueous ammonia to give the corresponding nucleoside analogs. The nucleoside analogs containing the cytosine (44) and 5-methylcytosine (43) bases were prepared from the uracil and thymine nucleoside analogs, respectively, by way of the 4-chloropyrimidinone intermediates (42 and 41). The synthesis of cis-3-aminocyclopentanemethanol (8) from norbornene by way of cis-1,3-cyclopentanedicarboxylic acid anhydride (3) is also described. In addition, the ease of nucleophilic opening of compound 3 is compared to the opening of camphoric anhydride (9), which contains a cis-vicinal substituent at position 2. The relative ease of opening of compound 3 is discussed with respect to the effect, observed in an earlier study, that a cis-vicinal acetoxy group has on the course of the nucleophilic opening of such anhydrides. The ¹H magnetic resonance spectra at 200 MHz of all of the synthetic intermediates and of the nucleoside analogs have been determined and discussed. The nucleoside analogs were screened for cell-growth inhibition using K-562 cells. Nucleoside analogs having the 2-thiouracil (33), 2-thiothymine (31), cytosine (44), and 5-methylcytosine (43) bases showed some growth inhibition with activity 150 to 300 times lower than that shown by 5-fluorouracil in this test system.