Synthetic approaches to a mononucleotide prodrug of cytarabine.

Synthetic pathways to a mononucleotide prodrug of cytarabine (Ara-C) bearing S-pivaloyl-2-thioethyl (tBuSATE) groups, as biolabile phosphate protections, are reported. Using a common phosphoramidite approach, two different kinds of nucleoside protecting groups have been investigated. During this study, we observed an intermolecular migration of the Boc protecting group in the course of the tert-butyldimethylsilyl ether cleavage using tetrabutyl ammonium fluoride.

Pyrazole related nucleosides 5. Synthesis and biological activity of 2'-deoxy-2',3'-dideoxy- and acyclo-analogues of 4-iodo-1-beta-D-ribofuranosyl-3-carboxymethyl pyrazole (IPCAR).

Continuing our studies on the structure-activity relationships (SAR) of 4-iodo-1-beta-D-ribofuranosyl-3-carboxymethyl pyrazole (IPCAR), the ribofuranosyl moiety has been substituted with acyclic chains, namely 1-[(2-hydroxyethoxy)methyl]- and 1-[(1,3-dihydroxy-2-propoxy)methyl]-pyrazole derivatives (4, 5 and 8, 9 respectively), with the 2'-deoxy-beta-D-ribofuranosyl group (12 and 13) and finally with the 2',3'-dideoxy-D-glycero-pentofuranosyl-moiety (16 and 17). None of the new compounds display any interesting biological activity.

Prodrugs of Ara-CMP and Ara-AMP with a S-acyl-2-thioethyl (SATE) biolabile phosphate protecting group: synthesis and biological evaluation.

The bis(S-pivaloyl-2-thioethyl) phosphotriesters of Ara-C and Ara-A were synthesized as potential bioreversible mononucleotide prodrugs. Some N- and O-acylated derivatives were also prepared with the aim to modify the lipophilicity of the title pronucleotides. Compounds were tested for their antitumor/antiviral activity against a variety of tumor cells and viruses.

Synthesis and biological evaluation of a series of substituted pyrazolo[3,4-d]-1,2,3-triazoles and pyrazolo[3,4-d]oxazoles.

In view of the biological relevance of triazole-based heterocyclic structures as antifungal, antiviral, and antitumor agents, we have synthesized a series of substituted pyrazolo[3,4-d]-1,2,3-triazoles (2e-h, 2j, 4b) which we evaluated for their cytostatic and antiviral (HIV-1 included) activity and for their capability to inhibit the multiplication of various human pathogenic fungi and bacteria. Moreover, the biological activities of a few compounds, namely pyrazolo[3,4-d]oxazoles (3a-e) and pyrazolo[3,4-d]-1,2,3-triazoles (2a-d, 4a, 5), previously obtained by us but not investigated for their biological activity, were also studied. Only compounds 3a-e were endowed with a significative antiproliferative activity on the human lymphoblastoid cell line MT-4 cells. All pyrazole derivatives proved ineffective in protecting cell cultures against the HIV-1-induced cytopathogenicity, and none of the compounds was active against the bacteria and fungi tested.

Enzymatic synthesis of 2'-O-acyl prodrugs of 1-(beta-D-arabinofuranosyl)-5(E)-(2-bromovinyl)uracil and of 2'-O-acyl-araU, -araC and -araA.

Pig liver esterase (EC 3.1.1.1) catalysed regioselective hydrolysis of 1-(2,3,5-tri-O-acyl-beta-D-arabinofuranosyl)uracil, -cytosine and -adenine to give the corresponding 2'-monoesters effectively and in high yield. This methodology enabled the preparation of 1-(2-O-acyl-beta-D-arabinofuranosyl)-5-[(E)-(2-bromovinyl)]uracil prodrugs which, although slightly less active than the parent 1-(beta-D-arabinofuranosyl)-5-(E)-(2 bromovinyl)uracil (sorivudine; BV-araU), were strongly active in vitro against varicella-zoster virus (ED50 2.4-45 ng/ml). The retarded rates of enzymatic hydrolysis of the 2'-esters imply that they might function as lipophilic prodrugs, leading to increased plasma and cellular concentrations. In view of the marked in vitro activity, they represent an interesting approach to arabinofuranosyl nucleoside prodrugs with improved pharmacokinetics and enzymatic stability.

Retinoic acid conjugates as potential antitumor agents: synthesis and biological activity of conjugates with Ara-A, Ara-C, 3(2H)-furanone, and aniline mustard moieties.

In a dual targeting approach, to explore the ability of tretinoin (all-trans-retinoic acid) to behave as a covalent carrier for cytotoxic entities, conjugates of retinoic acid with a few representative molecules, being important examples of antitumor pharmacophores (i.e., nucleoside analogues and alkylating agents), have been synthesized and tested for their cytostatic and differentiating activity. All compounds were stable to in vitro hydrolysis in human plasma and more lipophilic than the parent compounds, thus consenting enhanced uptake into the cells. Among the nucleoside analogues the Ara-C derivatives 3 and 6 and the Ara-A derivative 7 proved the most cytostatic (IC50 < 0.32 microgram/mL) resulting from 25- to > 144-fold more active (Ara-A derivatives) or at least as equally active (Ara-C derivatives) as compared to the parent nucleosides. Compound 3, endowed with a highly lipophilic silyl moiety at the 3' and 5' positions, showed the highest differentiating activity (54% and 44% differentiated HL-60 cells at 0.2 and 0.05 microgram/mL respectively). With regard to the retinoic acid conjugates of alkylating agents, compound 10 was the most cytostatic agent (IC50 < 0.32 microgram/mL) and the most potent differentiating agent (33-34% at 0.32 and 0.08 microgram/mL). These structures may also be regarded as analogs of either retinoic acid or the cytotoxic compound.

Pyrazole-related nucleosides. 4. Synthesis and antitumor activity of some 1-tetrahydropyranyl-4-substituted pyrazoles.

Continuing our studies on the structure-activity relationships of some pyrazole nucleosides (1a-h) structurally related to ribavirin, tiazofurin and selenazofurin, we describe here the synthesis and antitumor/antiviral/antimicrobial activity of a new series of 1-tetrahydropyranyl-4-substituted pyrazoles. In this study, the tetrahydropyranyl moiety (THP), designed as a mimic of the glycosidic portion of the parent compounds 1a-h, has led to a few derivatives with moderate cytotoxic activity against leukemia/lymphoma and solid tumor-derived cell lines (IC50 14-100 microM). The compounds obtained through substitution of the ribofuranosyl moiety by the THP moiety were still active, the free heterocyclic bases were devoid of any activity.

Synthesis and cytotoxic activity of 6-vinyl- and 6-ethynyluridine and 8-vinyl-and 8-ethynyladenosine.

It is well-known that the introduction of vinyl and ethynyl moieties into nucleosides is of crucial importance for cytostatic, antiviral, or other biological activities. In this study 6- and 8-vinyl-and -ethynyluridine and -adenosine were prepared by a general procedure involving the palladium-catalyzed cross-coupling of trimethylsilylacetylene or vinyltributyltin. The introduction of a vinyl group at C-6 of uridine or an ethynyl group at C-8 of adenosine resulted in nucleoside derivatives showing cytostatic activity against several murine and/or human tumor cell lines. Interestingly, 8-vinyladenosine had pronounced selective inhibitory effects on human (Molt/4F and MT-4) versus murine (L1210 and FM3A) tumor cell lines.

Geiparvarin analogues. 4. Synthesis and cytostatic activity of geiparvarin analogues bearing a carbamate moiety or a furocoumarin fragment on the alkenyl side chain.

As a continuation of previous studies on the synthesis and antitumor activity of geiparvarin analogues bearing a carbamate moiety in the alkyl side chain, a series of N-substituted [(E)-3-(4,5-dihydro-5,5-dimethyl-4-oxo-2-furanyl)-2- butenyl]carbamates (15a-f) were synthesized and tested with the objective to investigate the reason for the marked difference of cytostatic activity found between alkyl and phenyl derivatives. A series of compounds, characterized by different physicochemical properties, were designed in order to study this hypothesis. Moreover, to further investigate the modification of the alkenyl side chain, (E)- and (Z)-[2-(4,5-dihydro-5,5-dimethyl-4-oxo-2-furanyl)propenyl]-7H-furo[3,2- g][1]benzopyran-7-one (11a,b) were synthesized, the latter compounds being the combination of two units, namely, the 3(2H)-furanone ring system endowed with potent alkylating properties and the furocoumarin portion which binds to DNA resulting in potential DNA-targeted alkylating agents. The compounds were tested for their cytostatic activity against proliferation of murine (L1210) and human (Molt/4, CEM, or MT-4) tumor cells. The highest cytostatic activity found within both series of carbamic derivatives (15a-d,k and 15e,g-j) was associated with the highest global lipophilicity. With regard to compounds 11a,b, the cytostatic activity of (Z)-furocoumarin 11b might be related to a specific interaction with DNA (i.e., intercalation).

Pyrazole-related nucleosides. Synthesis and antiviral/antitumor activity of some substituted pyrazole and pyrazolo[4,3-d]-1,2,3-triazin-4-one nucleosides.

Several pyrazole and pyrazolo[4,3-d]-1,2,3-triazin-4-one ribonucleosides were prepared and tested for antiviral/antitumor activities. Appropriate heterocyclic bases were prepared by standard methodologies. Glycosylation of pyrazoles 6a-e,g,i and of pyrazolo[4,3-d]-1,2,3-triazin-4-ones 12f-1 mediated by silylation with hexamethyldisilazane, with 1-beta-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose, gave in good yields the corresponding glycosides 7a-e,g, 8g,i, 13f,h,k, and 14f, but could not be applied to compounds 12g,i,j,l. To overcome this occurrence, a different strategy involving the preparation, diazotization, and in situ cyclization of opportune pyrazole glycosides 9 and 10 was required. Moreover derivatives having the general formula 5 were considered not only as synthetic intermediates in the synthesis of 3 but also as carbon bioisosteres of ribavirin 4. All compounds were evaluated in vitro for cytostatic and antiviral activity. The pyrazolo[4,3-d]-1,2,3-triazin-4-one nucleosides that resulted were substantially devoid of any activity; only 15h,k showed a moderate cytostatic activity against T-cells. However, pyrazole nucleosides 9b,c,e were potent and selective cytotoxic agents against T-lymphocytes, whereas 9e showed a selective, although not very potent, activity against coxsackie B1.

New isoxazole derivatives of retinoids: synthesis and activity on growth and differentiation of tumor cells.

The effects of several newly synthesized isoxazole analogues of retinoids on differentiation and proliferation of 'in vitro' cultured tumor cell lines are reported. Some of the tested compounds exhibit significative differentiating action, inducing adipogenic conversion of the Chinese hamster FH06T1-1 cell line in a range of 2-10 times the activity of retinoic acid and retinol. In addition, most of the compound tested display antiproliferative activity comparable to that of natural retinoids. The reported data could be of interest for experimental anticancer therapy.

Geiparvarin analogues. 2. Synthesis and cytostatic activity of 5-(4-arylbutadienyl)-3(2H)-furanones and of N-substituted 3-(4-oxo-2-furanyl)-2-buten-2-yl carbamates.

In an attempt to determine some of the structural features of geiparvarin (1) that account for its cytostatic activity in vitro, a series of geiparvarin analogues (10a-i, 1, 12, and 14-16) which contain novel modifications in the region of the olefinic double bond and of the coumarin moiety have been designed and synthesized. Among the derivatives containing a carbamate moiety, only the analogues containing a carbamate group linked to an alkyl moiety 10b-i were endowed with potent cytostatic activity, whereas the corresponding benzene derivative 10a was devoid of any antiproliferative activity. 6-Methoxygeiparvarin 101 proved equally effective as geiparvin (1), while compounds containing an additional double bond at the side chain (12 and 14-16) were invariably 5-100-fold less effective than geiparvarin. Diene derivative 15, bearing a coumarin moiety, was essentially inactive against murine (L1210, FM3A) tumor cells but exhibited good activity against human (Molt/4F, MT-4) tumor cells.