Pteridines Part CXXI: Protection of (6R)-5,6,7,8-Tetrahydro-L-biopterin

A series of new (6R)-5,6,7,8-tetrahydo-l-biopterin derivatives have been synthesised and characterised by elemental analyses and UV and NMR spectroscopy.

Nitroimidazoles Part 7. Synthesis and Anti-HIV Activity of New 4-Nitroimidazole Derivatives

Reverse transcriptase enzyme (RT) is an attractive target for the development of new drugs useful in AIDS therapy and HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs), and offers the possibility of generating structures of increased potency. On this basis, a series of 4-oxo-3-phenyl-2- (phenylimino)thiazolidin-5-ylidene, 3-hydroxypropyl, 3-azidopropyl, and 3-aminopropyl derivatives of 1-benzyl-2-ethyl-4-nitroimidazoles 6-8, as well as the substituted 1,2,3-triazolo analogs 12-14, the diazepam 15 and carboxamide derivatives 16 and 17 were synthesized. All compounds have been evaluated for their anti-HIV activity

Synthesis of 7-Acyl-2,4-disubstituted Pteridines by Radical Nucleophilic Substitution and Displacement Reactions

2,4-Disubstituted pteridine derivatives (1-3) react with acyl radicals very selectively in position 7 by a nucleophilic Substitution mechanism (4-10). Oxidation of the 2-methylthio group proceeds with m-chloroperbenzoic acid in good yields to the corresponding 7-acyl-2-methylsulfonyl-4-aminopteridines (11-16). The methylsulfonyl group can easily been displaced by nucleophiles such as aliphatic amines (27, 29, 32-42, 45), cyclic amines (56- 61), aromatic amines (30, 31) and amino acids (43-54). Oxygen nucleophiles lead to 7-acyl-isopterin derivatives (62-66). The acyl side-chain is also prone to structural modifications leading to the corresponding secondary alcohols on NaBH4 reduction (74-77) or to imino derivatives on reactions with amines (67-73) which can analogously been reduced to 2,4-disubstituted 7-( l-aminoalkyl)pteridines (80-85). An interesting H-shift was observed during heating of 32, 78 and 79 with benzylamine leading not to the benzylimines but the isomeric benzylideneamino derivatives 86-88. Various acetylations by acetic anhydride (AC2O) gave 89-93 and reduction of the pyrazine moiety to the 5,6,7,8-tetrahydro-pteridine derivatives 94-96 proceeded in the expected manner. The characterization of ther newly synthesized pteridine derivatives was performed by 1H-NMR spectra, UV-spectra and elemental analyses. Measurements of the basic pKa values of a selection of 2,4,7-trisubstituted pteridines were pteridines to characterize the dication, monocation and the neutral species by their UV-spectra.

Pteridines, CXVI. (1) Synthesis and Reactivity of 6-Substituted l,3-Dimethyl-7-hydroxylumazines and 7-Substituted l,3-Dimethyl-(5H)-lumazin-6-ones

6-Substituted 1,3-dimethyl-7-hydroxylumazines (5-7) have been synthesized from 1,3-dimethyluracil-5,6- diamine (1) and a-ketoacid esters (2-4) under weakly acidic conditions. The isomeric 7-substituted 1,3-dimethyllumazin- 6-ones (18-20) resulted from a regioselective Boon synthesis starting from 6-chloro-l,3-dimethyl-5- nitrouracil (8) and α-aminoacid esters (9-11) in a three-step procedure. H202 oxidations led with 6 and 7 to the corresponding 5-N-oxides (21, 22) whereas in the lumazin-6-onc scries only the 7-phenyl derivative (20) reacted also at N-5 position forming a cyclic hydroxamic acid (23). The newly synthesized compounds have been characterized by elemental analyses,1H-NMR and UV spectra based upon pKa-determinations.

Aldol-type and Claisen Condensation Reactions of 1,3,6- and 1,3,7-Trimethyllumazines

Various side-chain modifications of 6- and 7-substituted 1,3-dimethyl-lumazines are described. Wittig reactions with 1.3-dimelhyllumazin-6- (13) and 1,3-dimethyllumazin-7-yl-methyltriphenyIphosphonium bromide (10) Icad to styryl derivates (8, 9, 14) as well as a variety of structural analoges 15 - 27. Compound 10 could be converted by DBU in the stable 1,3-dimethyllumazin-7-yl-triphenylphosphoniumylide (11). 1,3.6-Trimethyl- (1) and 6-benzyl 1,3-dimethyllumazine (29) have been subject for Claisen-condensations with etbyl Oxalate to give 28 and 30 1,3-Dimethyllumazme-6-carbonylchloride (33) reacted well with the ethoxy-magnesium salt of ethyl malonatc. ethyl cyanoacctate, ethyl acetacetate and malononitrilc to form elongated side-chains (34 - 37).

Pteridines CVIII Reactions of 6, 7-Dichloro-I, 3-dimethyllumazine with Sulfur-Nucleophiles

6,7-Dichloro-1,3-dimethyllumazine (1) and various 6-chloro-7-O-, S- and N-subst.-1,3-dimethyllumazines (2-7) react under relatively mild reaction condiditions with S-nucleophiles to the corresponding 6-mercapto derivatives 8-16. Treatment of 1 with sodium benzylmercaptide at room temperature led to di-( 6- chloro-1,3-dimethyllumazine-7-yl)sulfide (17) whereas thiourea caused transformation to the corresponding 7,7-disulfide 18. 7-Mercapto-1,3-dimethyl-6(5H)lumazinethione (12) can be modified widely by alkylations to open-chain (21-23, 27-29) or cyclic 6,7-bis-alkylthio derivatives (24-26) and acylations with phosgene and thiophosgene, respectivly, gave the derivatives 36 and 37 of the new 1 ,3-dithiolo[ 4,5-g]pteridine ring system. Ribosylation of 12 afforded a 6,7-bis-S-riboside (40) in high yield.

Pteridines CX

A series of new 6-substituted 2,4-diaminopteridines (3-23) and pterins (26-43) have been synthesized by nucleophilic displacement reactions at the side chain of 6-bromomethyl-2,4-diaminopteridine (2) and 6- bromomethylpterin (25) using various types of 0-, N- and S-nucleophiles. Acid and base hydrolyses allow easy conversion of the 2,4-diaminopteridines (3-5, 7, 9, 10, 12, 19-21 and 23) into the corresponding pterins (26-32, 39-42). Acylations take place at the amino as well as at the functional groups in the side chain (44-46). A versatile protection of the amino group in pterins is its transformation into the N ,N -dimethylaminomethylcnimino function by amide-acetals (47, 50) allowing subsequently selective acylations at the side chain (48, 49).

Nucleotides part LXXX: Synthesis of 3'-O fluorescence labeled thymidine derivatives and their 5'-O-triphosphates

A new labeling technique attaching a fluorescent pteridine derivative (3, 5) via a linker onto the 3'-OH group of 5'-O-dimethoxytritylthymidine (7) was developed to lead to the conjugates 8 and 11. After detritylation to give 9 and 12, the final conversion into the corresponding 5'-triphosphates (13, 14), which were isolated as sodium salts, was performed by known methods.

Nitrosation of N-methyl derivatives of uric acid and their transnitrosation ability to N-acetylcysteine

When 1,3-dimethyluric acid was treated with a nitric oxide donor, diethylamine NONOate, in an aerobic neutral solution and the reaction was analyzed by HPLC, 1,3-dimethyluric acid was consumed to yield a nitrosated derivative, which decomposed with a half-life of 17.9 min at pH 7.4 and 37 degrees C. When 1,3,7-trimethyluric acid was treated with diethylamine NONOate, no consumption of 1,3,7-trimethyluric acid was observed. However, in the reaction of N-acetylcysteine with diethylamine NONOate, the yield of N-acetyl-S-nitrosocysteine increased by the addition of 1,3,7-trimethyluric acid as well as 1,3-dimethyluric acid. For 1,3,7,9-tetramethyluric acid, no consumption in the reaction with diethylamine NONOate and no effect on the S-nitrosation were observed. These results suggest that 1,3-dimethyluric and 1,3,7-trimethyluric acids are both nitrosated by diethylamine NONOate on the nitrogen atom of their oxoimidazole ring, although the half-life of the nitrosated 1,3,7-trimethyluric acid is too short to detect by HPLC. Consequently, these two acids can act as vehicles of nitric oxide.

Improved synthesis of oligodeoxyribonucleotides

An improved synthesis of oligodeoxyribonucleotides was achieved with NPE- and NPEOC-protected phosphoramidites leading to easier and time-saving purification and isolation of the gene fragments.

Nucleosides part LXVI I: synthesis of 4-amino-7(8H)pteridinone-N8-nucleosides-structural analogs of adenosine

Various 4-amino-7(8H)pteridones (6, 12, 14, 15, 20, 22) have been glycosylated with 1-chloro-2'-deoxy-D-ribofuranose derivatives (25, 26) applying the new DBU-salt method to form the N(8)-2'-deoxy-D-ribofuranosides (27-36) which can be regarded as 2'-deoxyadenosine analogs. Analogously reacted the 2-N,N-dimethyl-amino-methyleneimino-7(8H)pteridones (43-48) to give preferentially the corresponding N(8)-beta-D-anomers (49-55). Ribosylation with 1-bromo-2,3,5-tri-O-benzoyl-a-D-ribofuranose (56) proceeded as well with 6, 12, 15, 45, and 46 to yield to N(8)-beta-D-ribofuranosides 57-61. Sugar deprotection led to the free N(8)-2'-deoxy-beta-D-ribofuranosides 37-42 and N(8)-beta-D-ribofurano-sides 62-65, respectively. Glycosylations via the silyl-method under Vorbruggen conditions led with 6, 12 and 15 to the same results, however, 4-amino-6-phenyl-7(8H)pteridone (14) reacted differently forming the N(1)-beta-D-ribofuranosides (71, 79) and the N(1)-2'-deoxy-alpha-and ss-D-ribofuranosides 73, 74, 77, 78. The assignments of the structures have been achieved by (1)H-NMR- and UV-spectra. C,H,N-elemental analyses account for the composition.

Intramolecular sensitization of photocleavage of the photolabile 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) protecting group: photoproducts and photokinetics of the release of nucleosides

Novel photolabile protecting groups based on the 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) group with a covalently linked thioxanthone as an intramolecular triplet sensitizer exhibit significantly enhanced light sensitivity under continuous illumination. Herein we present a detailed study of the photokinetics and photoproducts of nucleosides caged with these new protecting groups. Relative to the parent NPPOC group, the light sensitivity of the new photolabile protecting groups is enhanced by up to a factor of 21 at 366 nm and is still quite high at 405 nm, the wavelength at which the sensitivity of the parent compound is practically zero. A new pathway for deprotection of the NPPOC group proceeding through a nitroso benzylalcohol intermediate has been discovered to complement the main mechanism, which involves beta elimination. Under standard conditions of lithographic DNA-chip synthesis, some of the new compounds, while maintaining the same chip quality, react ten times faster than the unmodified NPPOC-protected nucleosides.

Plasma cytokine concentration changes induced by the antitumor agents dipterinyl calcium pentahydrate (DCP) and related calcium pterins

Analysis of plasma cytokine concentration changes determined that oral dosing with the antitumor agent (1:4 mol:mol) calcium pterin (CaPterin) increased plasma IL-10, decreased plasma IL-6, and decreased plasma IFN-gamma concentrations in nude mice with MDA-MB-231 xenograph tumors [Moheno, P., Pfleiderer, W., Dipasquale, A.G., Rheingold, A.L., Fuchs, D., 2008. Cytokine and IDO metabolite changes effected by calcium pterin during inhibition of MDA-MB-231 xenograph tumors in nude mice. Int. J. Pharm. 355, 238-248]. A further analysis, reported here, of plasma cytokine concentration changes in nude mice with the same tumor xenographs treated with dipterinyl calcium pentahydrate (DCP), (1:2 mol:mol) calcium pterin, and CaCl(2).2H(2)O has been carried out. The measured cytokines included: IL-1beta, IL-2, IL-4, IL-6, IL-10, IL-12, IFN-gamma, and TNF-alpha. The major preliminary findings from the analyses of these data are that (1) the overall relative tumor volumes for the treatments correlated significantly with a full study antitumor plasma cytokine pattern (fsAPCP), a composite measure consisting of decreased plasma IL-6 and increased IL-4 concentrations, and (2) DCP induces a significant threshold antitumor response strongly correlated to a derived DCP antitumor plasma cytokine pattern (DCP/APCP) consisting of plasma IL-12, IL-6, and IL-4 concentration changes. This DCP/APCP composite measure identifies plasma IL-12 concentration increases, plasma IL-6 concentration decreases, and plasma IL-4 concentration increases correlated to relative tumor volume decreases caused by DCP dosing. The finding that the novel calcium pterins and CaCl(2).2H(2)O treatments decrease plasma IL-6 concentrations corroborates the previous finding that CaPterin dosing decreases plasma IL-6 concentrations in this mouse/tumor system [Moheno, P., Pfleiderer, W., Dipasquale, A.G., Rheingold, A.L., Fuchs, D., 2008. Cytokine and IDO metabolite changes effected by calcium pterin during inhibition of MDA-MB-231 xenograph tumors in nude mice. Int. J. Pharm. 355, 238-248].

Universal 2-(4-nitrophenyl)ethyl and 2-(4-nitrophenyl)ethoxycarbonyl protecting groups for nucleosides and nucleotides

A universal blocking group strategy for nucleobases is described, using the 2-(4-nitrophenyl)ethyl (NPE) group for O4-T-, O4-U-, O6-dG-, and O6-G-protection as well as the 2-(4-nitrophenyl)ethoxycarbonyl (NPEOC) group for amino protection in dC, C, dA, A, dG, and G. Conversion into the corresponding 5'-O-dimethoxytrityl derivatives and subsequent phosphitylation to form the fully protected 3'-O-(2-cyanoethyl-N,N-diisopropylphosphoramidites) and 3'-O-(2-(4-nitrophenyl)ethyl-N,N-diisopropylphosphoramidites) produces a new class of interesting building blocks for oligonucleotide synthesis.

On the Mechanism of Intramolecular Sensitization of Photocleavage of the 2-(2-Nitrophenyl)propoxycarbonyl (NPPOC) Protecting Group

A spectroscopic study of a variety of covalently linked thioxanthone(TX)-linker-2-(2-nitrophenyl)propoxycarbonyl(NPPOC)-substrate conjugates is presented. Herein, the TX chromophore functions as an intramolecular sensitizer to the NPPOC moiety, a photolabile protecting group used in photolithographic DNA chip synthesis. The rate of electronic energy transfer between TX and NPPOC was quantified by means of stationary fluorescence as well as nanosecond and femtosecond time-resolved laser spectroscopy. A dual mechanism of triplet-triplet energy transfer has been observed comprising a slower mechanism involving the T1(pipi*) state of TX with linker-length-dependent time constants longer than 20 ns and a fast mechanism with linker-length-dependent time constants shorter than 3 ns. Evidence is provided that the latter mechanism is due to energy transfer from the T2(npi*) state which is in fast equilibrium with the fluorescent S1(pipi*) state. In the case of direct linkage between the aromatic rings of TX and NPPOC, the spectroscopic properties are indicative of one united chromophore which, however, still shows the typical NPPOC cleavage reaction triggered by intramolecular hydrogen atom transfer to the nitro group.

Inhibition of HIV type 1 replication in CD4+ and CD14+ cells purified from HIV type 1-infected individuals by the 2-5A agonist immunomodulator, 2-5A(N6B)

Two major interferon (IFN)-mediated antiviral defense enzymes are double-stranded (ds)RNA-dependent 2',5'-oligoadenylate (2-5A) synthetase (2-5OAS) and p68 kinase (PKR). When activated by dsRNA, 2-5OAS synthesizes 2-5A, which binds to and activates RNase L. Activated RNase L hydrolyzes single-stranded viral RNA, thereby inhibiting viral protein synthesis. HIV-1 inhibits the IFN-mediated intracellular antiviral pathways. We have reported the synthesis and characterization of a nuclease-resistant 2-5A agonist (2-5A(N6B)) that overcomes the HIV-1 induced blockades by restoring the 2-5OAS/RNase L antiviral pathway (Homan JW, et al., J Acquir Immune Defic Syndr 2002;30:9-20). The objective of this study was to test the effect of 2-5A(N6B) on chronically infected CD4(+) T lymphocytes and CD14(+) monocytes derived from HIV-1-seropositive individuals. Wild-type HIV-1 replication was effectively inhibited by 2-5A(N6B) in CD4(+) T lymphocytes and CD14(+) monocytes purified from HIV-1 seropositive individuals (n = 18) compared to untreated cells. We also assessed the cytotoxicity of 2-5A(N6B) and report that 2-5A(N6B) exerts its anti-HIV-1 activity with no evidence of cytotoxicity (IC(90) > 100,000 nM). Furthermore, 2-5A(N6B) did not alter the cellular RNA profile, affect CCR5 or CXCR4 coreceptor expression, or activate caspase-dependent apoptosis. Evidence is also provided to show that 2-5A(N6B), and naturally occurring 2-5A(4), act as ligands to activate human Toll-like receptor 4. These results indicate that the 2-5A agonist 2-5A(N6B) has the potential to enhance host cell innate and acquired immune defense mechanisms against HIV-1 infection.

Specific interaction of the diastereomers 7(R)- and 7(S)-tetrahydrobiopterin with phenylalanine hydroxylase: implications for understanding primapterinuria and vitiligo

Pterin-4a-carbinolamine dehydratase (PCD) is an essential component of the phenylalanine hydroxylase (PAH) system, catalyzing the regeneration of the essential cofactor 6(R)-L-erythro-5,6,7,8-tetrahydrobiopterin [6(R)BH4]. Mutations in PCD or its deactivation by hydrogen peroxide result in the generation of 7(R,S)BH4, which is a potent inhibitor of PAH that has been implicated in primapterinuria, a variant form of phenylketonuria, and in the skin depigmentation disorder vitiligo. We have synthesized and separated the 7(R) and 7(S) diastereomers confirming their structure by NMR. Both 7(R)- and 7(S)BH4 function as poor cofactors for PAH, whereas only 7(S)BH4 acts as a potent competitive inhibitor vs. 6(R)BH4 (Ki=2.3-4.9 microM). Kinetic and binding studies, as well as characterization of the pterin-enzyme complexes by fluorescence spectroscopy, revealed that the inhibitory effects of 7(R,S)BH4 on PAH are in fact specifically based on 7(S)BH4 binding. The molecular dynamics simulated structures of the pterin-PAH complexes indicate that 7(S)BH4 inhibition is due to its interaction with the polar region at the pterin binding site close to Ser-251, whereas its low efficiency as cofactor is related to a suboptimal positioning toward the catalytic iron. 7(S)BH4 is not an inhibitor for tyrosine hydroxylase (TH) in the physiological range, presumably due to the replacement of Ser-251 by the corresponding Ala297. Taken together, our results identified structural determinants for the specific regulation of PAH and TH by 7(S)BH4, which in turn aid in the understanding of primapterinuria and acute vitiligo.