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ParABS, an important DNA partitioning process in chromosome segregation, includes ParA (an ATPase), ParB (a parS binding protein) and parS (a centromere-like DNA). The homologous proteins of ParA and ParB in Helicobacter pylori are HpSoj and HpSpo0J, respectively. We analyzed the ATPase activity of HpSoj and found that it is enhanced by both DNA and HpSpo0J. Crystal structures of HpSoj and its DNA complexes revealed a typical ATPase fold and that it is dimeric. DNA binding by HpSoj is promoted by ATP. The HpSoj–ATP–DNA complex non-specifically binds DNA through a continuous basic binding patch formed by lysine residues, with a single DNA-binding site. This complex exhibits a DNA-binding adept state with an active ATP-bound conformation, whereas the HpSoj–ADP–DNA complex may represent a transient DNA-bound state. Based on structural comparisons, HpSoj exhibits a similar DNA binding surface to the bacterial ParA superfamily, but the archaeal ParA superfamily exhibits distinct non-specific DNA-binding via two DNA-binding sites. We detected the HpSpo0J–HpSoj–DNA complex by electron microscopy and show that this nucleoid-adaptor complex (NAC) is formed through HpSoj and HpSpo0J interaction and parS DNA binding. NAC formation is promoted by HpSoj participation and specific parS DNA facilitation.

This study presents structure and function of the sodium-dependent phosphate transporter, TmPiT-Pi/Na., Inorganic phosphate (Pi) is a fundamental and essential element for nucleotide biosynthesis, energy supply, and cellular signaling in living organisms. Human phosphate transporter (hPiT) dysfunction causes numerous diseases, but the molecular mechanism underlying transporters remains elusive. We report the structure of the sodium-dependent phosphate transporter from Thermotoga maritima (TmPiT) in complex with sodium and phosphate (TmPiT-Na/Pi) at 2.3-angstrom resolution. We reveal that one phosphate and two sodium ions (Pi-2Na) are located at the core of TmPiT and that the third sodium ion (Nafore) is located near the inner membrane boundary. We propose an elevator-like mechanism for sodium and phosphate transport by TmPiT, with the TmPiT-Na/Pi complex adopting an inward occluded conformation. We found that disease-related hPiT variants carry mutations in the corresponding sodium- and phosphate-binding residues identified in TmPiT. Our three-dimensional structure of TmPiT provides a framework for understanding PiT dysfunction and for future structure-based drug design.

Spo0J (stage 0 sporulation protein J, a member of the ParB superfamily) is an essential component of the ParABS (partition system of ParA, ParB, and parS)-related bacterial chromosome segregation system. ParB (partition protein B) and its regulatory protein, ParA, act cooperatively through parS (partition S) DNA to facilitate chromosome segregation. ParB binds to chromosomal DNA at specific parS sites as well as the neighboring nonspecific DNA sites. Various ParB molecules can associate together and spread along the chromosomal DNA. ParB oligomer and parS DNA interact together to form a high-order nucleoprotein that is required for the loading of the structural maintenance of chromosomes proteins onto the chromosome for chromosomal DNA condensation. In this report, we characterized the binding of parS and Spo0J from Helicobacter pylori (HpSpo0J) and solved the crystal structure of the C-terminal domain truncated protein (Ct-HpSpo0J)-parS complex. Ct-HpSpo0J folds into an elongated structure that includes a flexible N-terminal domain for protein-protein interaction and a conserved DNA-binding domain for parS binding. Two Ct-HpSpo0J molecules bind with one parS. Ct-HpSpo0J interacts vertically and horizontally with its neighbors through the N-terminal domain to form an oligomer. These adjacent and transverse interactions are accomplished via a highly conserved arginine patch: RRLR. These interactions might be needed for molecular assembly of a high-order nucleoprotein complex and for ParB spreading. A structural model for ParB spreading and chromosomal DNA condensation that lead to chromosome segregation is proposed.

Glucoamylases are responsible for hydrolysis of starch and polysaccharides to yield β-d-glucose. Rhizopus oryzae glucoamylase (RoGA) is composed of an N-terminal starch binding domain (SBD) and a C-terminal catalytic domain connected by an O-glycosylated linker. Two carbohydrate binding sites in RoSBD have been identified, site I is created by three highly conserved aromatic residues, Trp47, Tyr83, and Tyr94, and site II is built up by Tyr32 and Phe58. Here, the two crystal structures of RoSBD in complex with only α-(1,6)-linked isomaltotriose (RoSBD-isoG3) and isomaltotetraose (RoSBD-isoG4) have been determined at 1.2 and 1.3 A, respectively. Interestingly, site II binding is observed in both complexes, while site I binding is only found in the RoSBD-isoG4 complex. Hence, site II acts as the recognition binding site for carbohydrate and site I accommodates site II to bind isoG4. Site I participates in sugar binding only when the number of glucosyl units of oligosaccharides is more than three. Taken together, two carbohydrate binding sites in RoSBD cooperate to reinforce binding mode of glucoamylase with polysaccharides as well as the starch. Proteins 2014; 82:1079–1085. © 2013 Wiley Periodicals, Inc.

Uridylate kinase (UMPK; EC 2.7.4.22) transfers the γ-phosphate of ATP to UMP, forming UDP. It is allosterically regulated by GTP. Structures of Helicobacter pylori UMPK (HpUMPK) complexed with GTP (HpUMPK-GTP) and with UDP (HpUMPK-UDP) were determined at 1.8 and 2.5 Å resolution, respectively. As expected, HpUMPK-GTP forms a hexamer with six GTP molecules at its centre. Interactions between HpUMPK and GTP are made by the β3 strand of the sheet, loop β3α4 and the α4 helix. In HpUMPK-UDP, the hexameric symmetry typical of UMPKs is absent. Only four of the HpUMPK molecules bind UDP; the other two HpUMPK molecules are in the UDP-free state. The asymmetric hexamer of HpUMPK-UDP, which has an exposed dimer interface, may assist in UDP release. Furthermore, the flexibility of the α2 helix, which interacts with UDP, is found to increase when UDP is absent in HpUMPK-UDP. In HpUMPK-GTP, the α2 helix is too flexible to be observed. This suggests that GTP binding may affect the conformation of the α2 helix, thereby promoting UDP release.

Triosephosphate isomerase (TIM) catalyzes the interconversion between dihydroxyacetone phosphate and D-glyceraldehyde-3-phosphate in the glycolysis-gluconeogenesis metabolism pathway. The Helicobacter pylori TIM gene (HpTIM) was cloned, and HpTIM was expressed and purified. The enzymatic activity of HpTIM for the substrate GAP was determined (K(m) = 3.46 +/- 0.23 mM and k(cat) = 8.8 x 10(4) min(-1)). The crystal structure of HpTIM was determined by molecular replacement at 2.3 A resolution. The overall structure of HpTIM was (beta/alpha)beta(beta/alpha)(6), which resembles the common TIM barrel fold, (beta/alpha)(8); however, a helix is missing after the second beta-strand. The conformation of loop 6 and binding of phosphate ion suggest that the determined structure of HpTIM was in the "closed" state. A highly conserved Arg-Asp salt bridge in the "DX(D/N)G" motif of most TIMs is absent in HpTIM because the sequence of this motif is "(211)SVDG(214)." To determine the significance of this salt bridge to HpTIM, four mutants, including K183S, K183A, D213Q, and D213A, were constructed and characterized. The results suggest that this conserved salt bridge is not essential for the enzymatic activity of HpTIM; however, it might contribute to the conformational stability of HpTIM.

Virus isolates resistant to 1-[(2-hydroxyethoxy) methyl]-6-(phenylthio)thymine (HEPT) and a highly potent HEPT derivative, [1-benzyloxymethyl-5-ethyl-6-(α-pyridylthio)uracil] (NSC 648400, E-BPTU), were selected in cell culture. Cross-resistance evaluation indicated that the two drug resistant virus isolates were phenotypically distinct from one another although each of the virus isolates was resistant to both of the HEPT derivatives The virus isolate resistant to NSC 648400 had a single amino acid change in the reverse transcriptase (Y181C) which resulted in cross-resistance to all of the nonnucleoside reverse transcriptase inhibitors evaluated, with the exception of calanolide A. The NSC 648400-resistant virus isolate exhibited 15-fold enhanced sensitivity to calanolide A. The virus isolate selected in the presence of HEPT exhibited a single amino acid change (P236L) which was not cross- resistant to other nonnucleoside RT inhibitors tested with the exception of the two HEPT derivatives. This HEPT-resistant virus isolate exhibited enhanced sensitivity (5- to 10-fold) to thiazolobenzimidazole. We have used both virus isolates with defined single amino acid changes in the RT and bacterially expressed RTs with site-directed amino acid substitutions to test the effects of a wide variety of mutations on the activity of NSC 648400 Single mutations at amino acids 101, 103, 106, 181, or 236 yielded virus with high resistance (>20-fold) to NSC 648400, while lower levels of resistance were seen with mutations at amino acids 98, 100, or 108. These results suggest that several changes in the conformation of the nonnucleoside inhibitor binding site of the HIV-1 reverse transcriptase can affect the inhibitory activity of the HEPT class of compounds.

6-Arylthio and 6-arylselenoacyclonucleosides was synthesized and tested for the ability to inhibit replication of HIV-1. Lithiation of acyclonucleosides with LDA followed by reaction with the electrophiles phenyl disulfide, diphenyl diselenide, 2,2′-dipyrdyl disulfide or 2,2′-dipyridyl diselenide afforded 6-(arylthio or arylseleno)acyclonucleosides 5a-c, 6, 7, 9, 15a-c, 17a-c. Compounds 19a-c and 20a-c were obtained by deprotection of corresponding TBDMS derivatives. Dehydrated products 16a, and 18a-c were also formed during the reactions. 5-Ethyl-6-(α-pyridylthio or α-pyridylseleno) disubstituted acyclouracils 6 and 7 were more active against HIV-1 in both MT-2 and CEM-IW cell lines than AZT, DDC, DDI or D4T. The EC50 of 6 against HIV-1 in CEM-IW cell was in the nanomolar range with a therapeutic index of 1100.

Blends between poly(acrylic acid) and two different poly(oxyethylenes), (1) polyethylene glycol (PEG-1000) and (2) poly(oxyethylene) (20) sorbitan monooleate (Tween-80), were studied by differential scanning calorimetry. The glass transition temperatures, Tg, of the various compositions of these blends were found to follow Fox's equation. At room temperature, blends containing no more than 60% PEG-1000 were amorphous and exhibited only a single glass transition. For these blends with PEG-1000, the glass transition temperatures for the annealed samples were higher than for the quenched samples due to the formation of a PEG crystalline phase. It was also found that addition of an amorphous polymer such as poly(acrylic acid) significantly reduced the degree of crystallinity of a semicrystalline polymer such as poly(oxyethylene). The Tween-80 systems did not show phase separation at room temperature. The compatibility between this poly(acrylic acid) and this poly(oxyethylene) was attributed to hydrogen bonding and to the lower crystalline lattice energy of this poly(oxyethylene) through its effect on its ideal solution solubility. © 1993 John Wiley & Sons, Inc.

5-Benzyl and 5-benzyloxybenzyl-substituted 3′-azido-2′,3′-dideoxyuridine, (8a and 8b), 3′-halogeno-2′,3′-dideoxyuridine, 9a, 9b, 10a, 10b, 11a and 11b, and 2′,3′-dideoxyuridine, 12a and 12b, of Scheme I were synthesized as potential anti AIDS agents. Synthesis of epimers of 8a and 8b, 5-benzyl- and 5-benzyloxybenzyl-1-(3′-azido-2′,3′-dideoxy-β-D-threo-pentafuranosyl)uracil, 15a and 15b, and 5-benzyl- and 5-benzyloxy-5′-azido-2′,5′-dideoxyuridine, 16a and 16b, shown in Scheme II, were also reported.

6-Arylthio and 6-arylselenoacyclonucleosides was synthesized and tested for the ability to inhibit replication of HIV-1. Lithiation of acyclonucleosides with LDA followed by reaction with the electrophiles phenyl disulfide, diphenyl diselenide, 2,2′-dipyrdyl disulfide or 2,2′-dipyridyl diselenide afforded 6-(arylthio or arylseleno)acyclonucleosides 5a-c, 6, 7, 9, 15a-c, 17a-c. Compounds 19a-c and 20a-c were obtained by deprotection of corresponding TBDMS derivatives. Dehydrated products 16a, and 18a-c were also formed during the reactions. 5-Ethyl-6-(α-pyridylthio or α-pyridylseleno) disubstituted acyclouracils 6 and 7 were more active against HIV-1 in both MT-2 and CEM-IW cell lines than AZT, DDC, DDI or D4T. The EC50 of 6 against HIV-1 in CEM-IW cell was in the nanomolar range with a therapeutic index of 1100.

1'-Halogenomethyl, 1'-azidomethyl and 1'-disubstituted aminomethyl derivatives of BAU (5-benzylacyclouridine) and BBAU (5-benzyloxybenzylacyclouridine) were synthesized in the course of our studies of benzylacyclouridines. Two new and more convenient preparations of the previously known aminomethyl-and hydroxyymethyl-parent compounds of these two series, AM-BAU, AM-BBAU and HM-BBAU are also reported. These compounds were synthesized during a search for potential antiviral agents and pyrimidine phosphorylase inhibitors

5-Benzyl and 5-benzyloxybenzyl-substituted 3′-azido-2′,3′-dideoxyuridine, (8a and 8b), 3′-halogeno-2′,3′-dideoxyuridine, 9a, 9b, 10a, 10b, 11a and 11b, and 2′,3′-dideoxyuridine, 12a and 12b, of Scheme I were synthesized as potential anti AIDS agents. Synthesis of epimers of 8a and 8b, 5-benzyl- and 5-benzyloxybenzyl-1-(3′-azido-2′,3′-dideoxy-β-D-threo-pentafuranosyl)uracil, 15a and 15b, and 5-benzyl- and 5-benzyloxy-5′-azido-2′,5′-dideoxyuridine, 16a and 16b, shown in Scheme II, were also reported.

Spermidine synthase (putrescine aminopropyltransferase, PAPT) catalyzes the transfer of the aminopropyl group from decarboxylated S-adenosylmethionine to putrescine during spermidine biosynthesis. Helicobacter pylori PAPT (HpPAPT) has a low sequence identity with other PAPTs and lacks the signature sequence found in other PAPTs. The crystal structure of HpPAPT, determined by multiwavelength anomalous dispersion, revealed an N-terminal β-stranded domain and a C-terminal Rossmann-like domain. Structural comparison with other PAPTs showed that HpPAPT has a unique binding pocket between two domains, numerous non-conserved residues, a less acidic electrostatic surface potential, and a large buried space within the structure. HpPAPT lacks the gatekeeping loop that facilitates substrate binding in other PAPTs. PAPTs are essential for bacterial cell viability; thus, HpPAPT may be a potential antimicrobial drug target for H. pylori owing to its characteristic PAPT sequence and distinct conformation. Proteins 2007. © 2007 Wiley-Liss, Inc.

Nucleoside analogues of uridine, 5-bromo-, 5-iodo-, and 5-fluorouridines, thymidine and cytidine were prepared by condensing appropriately substituted 2,4-dimethoxypyrimidines with an acyclic side chain in the form of a benzoylated halo-ether, and subsequent removal of the protecting benzoyl group in base. The 2′-O-p-tosylates of these nucleoside analogues could then be modified to 2′-halo-, azido-, and amino derivatives. Many of these compounds are competitive inhibitors of uridine phosphorylase in vitro, the most active being 5-methyl-1-(2′-hydroxyethoxymethyl)uracil.

A useful, facile procedure for preparing seleno-heterocyclic compounds is reported. Treatment of cAMP, AMP, adenosine, 2-aminoadenosine, adenine arabinoside and formycin with hydrogen selenide in aqueous pyridine at 65° for 1.5-5 days gave the corresponding seleno compounds in good yield, while these compounds were relatively inert to hydrogen sulfide. A reaction mechanism is proposed.

6-Chloro-9-(beta-D-arabinofuranosyl)purine served as an intermediate for the chemical synthesis of a series of 6-substituted selenopurine arabinosides. In an in vitro test using murine leukemic cells (L-5178Y) these 6-substituted selenopurine arabinosides showed some cytotoxicity. Lengthening the side chain had no effect on their cytotoxicity. Selenourea was a useful reagent for synthesizing selenopurines, selenopurine nucleosides, and selenopurine arabinoside under mild conditions.

The title compound crystallizes in the triclinic space group [Formula: see text] and the cell dimensions are a = 16.890(3), b = 9.586(2), c = 6.316(1) Å, α = 91.09(1), β = 93.50(1), γ = 93.04(1)°. X-ray intensity data were measured on a diffractometer, and the crystal structure was determined by direct methods. Least-squares refinement, which included all hydrogen atoms, converged at R = 0.056 for 3454 observed reflections. Adjacent six-membered rings are approximately perpendicular to one another. The glycosidic torsion angle [C(6)—N(1)—C(1′)—O(4′)] is 96.2(2)°. In the acyclic moiety, both C—OH bonds are gauche with respect to C(4′)—O(4′). The gauche conformation is also dominant in solution, as determined by high-resolution 1H nmr spectroscopy. Results of nuclear Overhauser experiments lead to conclusions about the flexibility of the molecule.

Eighty-seven pyrimidine base and nucleoside analogs were evaluated as inhibitors of uridine phosphorylase (UrdPase) and thymidine phosphorylase (dThdPase). These findings, together with an extensive literature review, have allowed construction of structure-activity relationships for the binding of ligands to UrdPase and dThdPase and provide a basis for the rational design of new inhibitors of these enzymes. Additionally, 2,6-pyridinediol and 6-benzyl-2-thiouracil have been identified as being potent inhibitors of UrdPase and dThdPase respectively.

Hydroxymethyl analogs of 5-benzylacyclouridine (BAU) and 5-benzyloxybenzylacyclouridine (BBAU) were synthesized by the condensation of appropriately blocked 2-(chloromethyl)glycerols with substituted 2, 4-dimethoxypyrimidines. The HM derivatives were found to be potent inhibitors of the enzyme uridine phosphorylase and to potentiate significantly the growth-inhibiting action of FdUrd in cell culture.

8-Bromoguanosine cyclic 3',5'-monophosphate, 8-bromoguanosine 5'-monophosphate, and 8-bromoguanosine served as intermediates for the chemical synthesis of a series of 8-substituted seleno cyclic nucleotides, nucleotides, and their nucleosides. Selenourea was found to be a useful reagent in synthesizing these seleno-substituted nucleoside, nucleotide, and cyclic nucleotide. A nucleic acid analyzer was used to study the hydrolysis of these cyclic nucleotides by phosphodiesterase. It was found that all of the 8-substituted selenoguanosine cyclic 3',5'-phosphates synthesized, except 8-MeSe-cGMP, were resistant to hydrolyze by phosphodiesterase. These 8-substituted seleno cyclic GMP derivatives showed some antitumor activities against murine leukemic cells (L5178Y) in vitro and in vivo.

Survival studies were performed in mice bearing Sarcoma 180 ascites tumor treated with 6-thio and 6-seleno analogs of guanine and guanosine. The selenium-containing analogs were somewhat superior to the sulfur-containing compounds in antitumor activity and therapeutic index. The formation of 6-SeGMP from 6-seleno-guanine (6-SeG) was demonstrated in Sarcoma 180 ascites cells. Guanine, 6-thioguanine (6-TG) and 6-SeG show comparable substrate activity whereas 8-azaguanine is a much poorer substrate for hypoxanthine-guanine phosphoribosyl transferase from Sarcoma 180 cells. Both 6-TG and 6-SeG are good substrates for purine nucleoside phosphorylase from Sarcoma 180 cells. Chemically and enzymatically synthesized 6-SeGMP behaved as a competitive inhibitor ( K i 1 × 10 −4 M) of erythrocytic and Sarcoma 180 guanylate kinases. Weak substrate activity was demonstrated in the presence of large amounts of erythrocytic guanylate kinase.

In attempts to increase the specificity of thiol agents and protect the genetic material of the cell, which is very sensitive to radiation damage, the synthesis of a group of compounds was undertaken in which cysteamine is attached through its amino group to a series of purine and pyrimidine components of nucleic acids. The 5-position of pyrimidines and the 8-position of purines seem well suited for the attachment of groups to be introduced into nucleic acids. Attempts were also made to introduce the bis( BETA -thioethyl) amino group into suitable carrier molecules to yield doublearmed cysteamines. While attempts to isolate bis-( BETA -mercaptoethyl)amine were unsuccessful, the oxidized form of the compound, 1,2-dithia-5-azepane was prepared in good yield. Thus, the preparation of N-substituted 1,2-dithia-5azepanes appeared feasible. A number of uracilyl compounds were prepared by reaction sequences which are shown. BETA -Benzylthioethylamine, prepared by the reaction of ethyleneimine with alpha - toluenethiol, was found to react with 5-bromouracil to yield 5-L BETA - benzylthioethylamino) uracil, This compound could also be obtained by the addition of alpha -toluenethiol to 5-( BETA -chloroethylamino)uracil (onearmed uracil mustard). Debenzylation with sodium in liquid ammonia resulted in the formation of 5-( BETA -mercaptoethylamino)uracil. Attempts to isolate themore » compound were unsuccessful; however, oxidation readily yielded its disulfide form. Bis( BETA -benzylthioethyl)amine reacted with 5bromouracil to form 5-bis( BETA - benzylthtoethylamino)uracil. An alternative synthesis of the compound involved the addition of the sodium salt of benzyl mercaptan to 5-bis( BETA chloroethylamino)uracil (uracil mustard). Reduction of the bis-benzylthio compound with sodium in liquid ammonia followed by air oxidation yielded N-(5- uracilyl)-1,2-dithta5-azepane. N,N'-bis(8-adeninyl)cystamine was prepared in annlogous fashion from 8-( BETA -benzylthioethylamino)adenine, which in turn was obtained by the reaction of 8bromoadenine with BETA -benzylthioethylamine. Difficulties were encountered in isolating mercaptans as such because of the rapidity of air oxidation. (P.C.H.)« less

The benzylacyclouridines, potent and specific inhibitors of mammalian uridine phosphorylase, were also found to be inhibitors of uridine phosphorylase but not thymidine phosphorylase from Escherichia coli. Competitive inhibition was observed in all cases and the most potent of these compounds was HM-BBAU (5-(3-benzyloxybenzyl)-1-[(2'-hydroxy-1'-hydroxymethyl)methyl]urac il) with a Ki value of 0.15 microM. The inhibitory potencies of these compounds parallel those obtained with enzymes from mammalian sources [Niedzwicki et al., Biochem. Pharmac. 31, 1857 (1982) and Naguib et al., manuscript in preparation] indicating that the structure of the active site of uridine phosphorylase from E. coli may resemble that of the mammalian enzyme.

In view of the effectiveness of aminoethyl mercaptan (cysteamine) and of 2-aminoethylisothiouronium (AET) salts in protecting animals against ionizing radiation, efforts were made to prepare even more active analogs of the compounds. Sulfur is considered to be essential to the radioprotective action of cysteamine analogs; however, the selenium analog of cysteamine can shield mice against radiation. Since the atomic radii of sulfur and of selenium are similar, sulfur and selenium analogs may be assumed to have the same ability of fit receptor sites. The selenium analog of AET was prepared by the reaction of selenourea with 2-bromoethylamine hydrobromide. Treatment of the selenouronium salt with NaOH yielded 2-selenoethylguanidine, which was isolated as the flavianate salt. The reaction of 2-aminoethylisoselenouronium hydrobromide with boiling water resulted in the formation of 2-aminoselenazoline. Through the reaction of 2- methylaminoethyl. 2dimethylaminoethyl, and 2-diethylaminoethyl halides with selenourea the corresponding 2-alkylaminoethyl selenouronium salts were obtained. Similarly, 3-aminopropylisoselenouronium hydrobromide was synthesized.

A new class of nucleoside analogs, the pyridimine acyclonucleosides, are competitive inhibitors of uridine phosphorylase but have no effect on thymicline phosphorylase, uridine kinase or thymidine kinase. The most potent of the series is acyclothymidine [5-methyl-1-(2′-hydroxyethoxymethyl)uracil] with a Ki value of 3 μM. Ki values of less than 30 μM were estimated for other analogs substituted at the 5-position of the pyrimicline ring. Extracts of xenografts of six human tumors were assayed for tissue levels of uricline phosphorylase and thymicline phosphorylase and for inhibition of 5-fluoro-2′-deoxyuridine (FUdR) phosphorolytic activity by acyclouridine [1-(2′-hydroxyethoxymethyl) uracil]. FUdR cleavage was inhibited most in those tissues in which the ratio of thymidine phosphorylase to uricline phosphorylase was low. Potential usage of these uricline phosphorylase inhibitors with the chemotherapeutic agent FUdR is discussed.

Various pyrimidine acyclonucleosides (l-(2'-hydroxyethoxymethyl)uracils) are specific inhibitors of uridine phosphorylase [Niedzwicki et al., Biochem. Pharmac. 30 , 2097 (1981)]. 5-Benzyluracils have also been shown to inhibit this enzyme [Baker and Kelley. J. med. Chem. 13 , 461 (1970); Woodman et al., Biochem. Pharmac . 29 ,1059 (1980)]. We have synthesized the acyclonucleoside analogs of 5-benzyluracil (BU) and 5-benzyloxybenzyluracil (BBU). These compounds, 5-benzyl-1-(2'-hydroxy-ethoxymethyl) uracil (BAU) and 5-( m -benzyloxybenzyl)-1-(2'-hydroxyethoxymethyl)uracil (BBAU), are potent inhibitors of uridine phosphorylase. K i values of 98 and 32 nM were estimated for BAU and BBAU respectively. These compounds are better inhibitors of uridine phosphorylase than BU ( K i = 1575 nM), BBU ( K i = 270 nM), and all other compounds previously tested, and they have no effect on thymidine phosphorylase, uridine-cytidine kinase, or thymidine kinase. Potential chemotherapeutic applications of BAU and BBAU are discussed.

6-Chloro-9-(β-D-arabinofuranosyl)purine served as an intermediate for the chemical synthesis of a series of 6-substituted selenopurine arabinosides. In an in vitro test using murine leukemic cells (L-5178Y) these 6-substituted selenopurine arabinosides showed some cytotoxicity. Lengthening the side chain had no effect on their cytotoxicity. Selenourea was a useful reagent for synthesizing selenopurines, selenopurine nucleosides, and selenopurine arabinoside under mild conditions.

Treatment of adenosine, 2-aminoadenosine, adenine arabinoside, formycin, 1-Me-AMP, cyclo-AMP, and 1-Me-cyclo-AMP with H2Se in aqueous pyridine gave the corresponding seleno compounds with good yield.

8-Bromoguanosine cyclic 3',5'-monophosphate, 8-bromoguanosine 5'-monophosphate, and 8-bromoguanosine served as intermediates for the chemical synthesis of a series of 8-substituted seleno cyclic nucleotides, nucleotides, and their nucleosides. Selenourea was found to be a useful reagent in synthesizing these seleno-substituted nucleoside, nucleotide, and cyclic nucleotide. A nucleic acid analyzer was used to study the hydrolysis of these cyclic nucleotides by phosphodiesterase. It was found that all of the 8-substituted selenoguanosine cyclic 3',5'-phosphates synthesized, except 8-MeSe-cGMP, were resistant to hydrolyze by phosphodiesterase. These 8-substituted seleno cyclic GMP derivatives showed some antitumor activities against murine leukemic cells (L5178Y) in vitro and in vivo.

Kinetic parameters for the phosphorolytic activity of uridine phosphorylase (UrdPase) from human and mouse livers have been determined. The values of these parameters are: K P i = 279.0 ± 66.0 μ M, K Urd = 242.0 ± 63.0 μ M and V max = 3940 ± 175 pmol/min/mg, and K P i = 76.0 ± 7.0 μ M, K Urd = 143.0 ± 9.0 μ M and V max = 293.0 ± 5.0 pmol/min/mg, for human and mouse livers respectively. Benzylacyclouridines, the specific inhibitors of UrdPase, and seventeen newly synthesized derivatives, modified at the pyrimidine ring, the benzyl moiety or the acycio tail, have been tested for their potency to inhibit UrdPase and thymidine phosphorylase (dThdPase) from both human and mouse livers. None inhibited dThdPase. In contrast, all of the compounds tested inhibited UrdPase. Competitive inhibition was observed in all cases. Several of the new compounds were superior in their inhibition of UrdPase to the parent compounds. The inhibitory potencies of these compounds with UrdPase from human liver roughly paralleled those obtained with UrdPase from mouse liver. The most potent of these compounds was AM-BBAU (aminomethyl-BBAU or 5-(3'-benzyloxybenzyl)-1-[(1'-aminomethyl-2'-hydroxy-ethoxy)methyl]uracil) with a K i value of 18 nM with UrdPase from mouse liver. Structure-activity relationships of the binding of these inhibitors of UrdPase are discussed.

6-Methylmercaptopurine ribonucleoside (MeMPR) is the most potent inhibitor known of PRPP amidotransferase, the first step in purine biosynthesis de novo. We have examined other 6-methylmercapto- and 6-methylselenopurine ribonucleosides for their ability to act as feedback inhibitors of this pathway as well as for their ability to form analog nucleotides. Methylmercaptopurine ribonucleoside (MeMPR), methylselenopurine ribonucleoside (MeSePR), and methylmercaptopyrazolo pyrimidine ribonucleoside (MeMPPR) were potent inhibitors (90 per cent), methylselenopyrazolo pyrimidine ribonucleoside (MeSePPR) was less potent (75 per cent), and methylselenoguanosine (MeSeGR) did not significantly inhibit this pathway. Large amounts of the corresponding 5'-monophosphate nucleosides were formed from MeMPR and MeMPPR, lesser amounts from MeSePPR and MeSePR and none from MeSeGR. The ability of 6-selenoguanine, its ribonucleoside and the α- and β-anomers of the deoxyribonucleoside were also examined as possible inhibitors of purine synthesis de novo. Further investigation is needed to determine if these compounds have significant activity as antineoplastic agents, but in any case they may lead to structural modifications which will produce active compounds.

Treatment of adenosine, 2-aminoadenosine, adenine arabinoside, formycin, 1-Me-AMP, cyclo-AMP, and 1-Me-cyclo-AMP with H2Se in aqueous pyridine gave the corresponding seleno compounds with good yield.