Synthesis of DNA fragments containing 2'-deoxy-4'-selenonucleoside units using DNA polymerases: comparison of dNTPs with O, S and Se at the 4'-position in replication.

4'-SelenoDNA fragments were synthesized for the first time using 4'-selenothymidine triphosphate (SeTTP) by taking advantage of its bioequivalence against DNA polymerases. DNA fragments each with a homologous element (O, S or Se) at the 4'-position of the thymidine units were effectively amplified using KOD Dash DNA polymerase.

New and Common Haplotypes Shape Genetic Diversity in Asian Tiger Mosquito Populations from Costa Rica and Panamá.

The Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae), is a vector of several human pathogens. Ae. albopictus is also an invasive species that, over recent years, has expanded its range out of its native Asia. Ae. albopictus was suspected to be present in Central America since the 1990s, and its presence was confirmed by most Central American nations by 2010. Recently, this species has been regularly found, yet in low numbers, in limited areas of Panamá and Costa Rica (CR). Here, we report that short sequences (∼558 bp) of the mitochondrial cytochrome oxidase subunit 1 (COI) and NADH dehydrogenase subunit 5 genes of Ae. albopictus, had no haplotype diversity. Instead, there was a common haplotype for each gene in both CR and Panamá. In contrast, a long COI sequence (∼1,390 bp) revealed that haplotype diversity (±SD) was relatively high in CR (0.72±0.04) when compared with Panamá (0.33±0.13), below the global estimate for reported samples (0.89±0.01). The long COI sequence allowed us to identify seven (five new) haplotypes in CR and two (one new) in Panamá. A haplotype network for the long COI gene sequence showed that samples from CR and Panamá belong to a single large group. The long COI gene sequences suggest that haplotypes in Panamá and CR, although similar to each other, had a significant geographic differentiation (Kst=1.33; P<0.001). Thus, most of our results suggest a recent range expansion in CR and Panamá.

Geographical Distribution of Aedes aegypti aegypti and Aedes aegypti formosus (Diptera: Culicidae) in Kenya and Environmental Factors Related to Their Relative Abundance.

The mosquito Aedes aegypti (L.) is the primary vector of various infectious viruses and is typified by a polymorphic color and abundance of white scales on the body. It has been conventionally separated into two subspecies, Ae. aeg. formosus (Walker) (Aaf) and Ae. aeg. aegypti (L.) (Aaa), with Aaf considered a 'sylvan' form and Aaa a 'domestic' form. Because the two subspecies show different susceptibilities to dengue viruses it is important to understand their distribution. In this study, we collected larvae from artificial and natural habitats in southern Kenya and reared them to adults to morphologically identify subspecies. We describe the geographical distribution and relative abundance of Aaa and Aaf in Kenya, and estimate the environmental factors associated with their distributions by GIS using climate and environment data. A total of 5,243 Ae. aegypti adults were collected from 249 sites, with Aaa accounting for 22% of the specimens. The relative abundance of Aaa was higher in coastal areas versus sites in western Kenya. Aaa abundance was also higher in urbanized than forested areas, which is consistent with known ecology. In contrast and inconsistent with previous studies, both Aaa and Aaf were sympatric in artificial and natural habitats. The high relative abundance of Aaa in coastal areas might derive from old populated cities, climate, and/or introduction from abroad.

Climate change is catchy--but when will it really hurt?

Concern and general awareness about the impacts of climate change in all sectors of the social-ecological-economic system is growing as a result of improved climate science products and information, as well as increased media coverage of the apparent manifestations of the phenomenon in our society. However, scales of climate variability and change, in space and time, are often confused and so attribution of impacts on various sectors, including the health sector, can be misunderstood and misrepresented. In this review, we assess the mechanistic links between climate and infectious diseases in particular, and consider how this relationship varies, and may vary according to different time scales, especially for aetiologically climate-linked diseases. While climate varies in the medium (inter-annual) time frame, this variability itself may be oscillating and/or trending on cyclical and long-term (climate change) scales because of regional and global scale climate phenomena such as the El-Nino southern oscillation coupled with global-warming drivers of climate change. As several studies have shown, quantifying and modelling these linkages and associations at appropriate time and space scales is both necessary and increasingly feasible with improved climate science products and better epidemiological data. The application of this approach is considered for South Africa, and the need for a more concerted effort in this regard is supported.

Mechanism-based design of inosine 5-monophosphate dehydrogenase inhibitors: synthesis and biological activities of 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and its derivatives.

Inosine 5 -monophosphate dehydrogenase (IMPDH) catalyzes the nicotinamide adenine dinucleotide (NAD)-dependent oxidation of inosine 5 -monophosphate (IMP) to xanthosine 5 -monophosphate (XMP), and is one of the key rate-determining enzymes of de novo guanine nucleotide biosynthesis in mammalian systems. Based on the proposed catalytic mechanism of IMPDH, we designed and synthesized 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (5b, EICAR) from 5-amino-1-beta-D-ribofuranosylimida-zole-4-carboxamide (AICAR) via palladium chemistry. EICAR is a potent cytostatic agent that inhibits various tumor cells in culture including human solid tumor cells in vitro and in vivo. EICAR also showed broad-spectrum antiviral activities, about 10- to 100-fold greater than those of ribavirin. An examination of the structure-activity relationships revealed that an alkynyl group, especially an ethynyl group at the 5-position, is important for its activity due to the inhibition of IMPDH. The mode of action of EICAR is also discussed.

Nucleosides and nucleotides. 96. Synthesis and antitumor activity of 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and its derivatives.

The palladium-catalyzed cross-coupling reaction of 5-iodo-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)imidazole-4- carboxamide (8) with various terminal alkynes in the presence of bis(benzonitrile)palladium dichloride in acetonitrile containing triethylamine gave the desired 5-alkynyl derivatives 9 in high yields. However, when (trimethylsilyl)acetylene was used, the only isolable product was the undesired dimer, 1,2-bis(4-carbamoyl-1-beta-D-ribofuranosylimidazol-5-yl)acetylene derivative 10a. To circumvent such dimer formation, the reaction was done with use of trimethyl-[(tributylstannyl)ethynyl]silane in the absence of triethylamine to afford the desired 5-(2-trimethylsilyl)ethynyl derivative 9a in good yield. Furthermore, the similar cross-coupling reaction of 5-iodo-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)imidazole-4-carboni tri le (12) with (trimethylsilyl)acetylene also afforded the desired nucleoside 13a. Deprotection of these compounds furnished 5-alkynyl-1-beta-D-ribofuranosylimidazole-4-carboxamides (6b-k) and -carbonitriles (14b-f). Among these, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (6b, EICAR) is the most potent inhibitor of growth of the various tumor cells in culture including human solid tumor cells. Preliminary results of in vivo antitumor activity against murine leukemias L1210 and P388 are also described.

Nucleosides and nucleotides. 123. Synthesis of 1-(2-deoxy-2-isocyano-beta-D-arabinofuranosyl)cytosine and related nucleosides as potential antitumor agents.

2'-Deoxy-2'-isocyano-1-beta-D-arabinofuranosylcytosine (8, NCDAC) has been synthesized as a potential antitumor antimetabolite from a corresponding 2'-azido-2'-deoxy-1-beta-D-arabinofuranosyluracil derivative 2a. Uracil and thymine analogues 6a and 6b of 8 were also prepared. Attempts to synthesize 2'-deoxy-2'-isocyanocytidine (14b) failed due to the insertion of the 2'-alpha isocyano group into the 3'-OH group, affording the 2',3'-oxazoline derivative 15b. Stability of the isocyano derivative 6a and 2',3'-oxazoline derivative 15a under basic and acidic conditions were examined. The isocyano group in 6a was stable in basic conditions but unstable even in weakly acidic conditions to furnish the corresponding 2'-beta formamide derivative 17. Compound 15a was easily hydrolyzed the corresponding 2'-alpha formamide derivative 16 on treatment with H2O at room temperature. The cytotoxicity of 8, 6a, and 6b was examined in mouse and human tumor cells in vitro and compared with that of ara-C. Of these nucleosides, 8 was moderately cytotoxic to these cell lines. In vivo antitumor activity of 8 against Lewis lung carcinoma cells was also investigated and 8 showed only moderate tumor volume inhibition.

Nucleosides and nucleotides. 200. Reinvestigation of 5'-N-ethylcarboxamidoadenosine derivatives: structure-activity relationships for P(3) purinoceptor-like proteins.

The non-P(1) and non-P(2) muscle relaxant effect of ATP in rabbit thoracic aorta has recently been attributed to a putative P(3) purinoceptor, which is activated by either adenosine or ATP. Since the physiological roles of this putative P(3) purinoceptor and of a new [(3)H]-5'-N-ethylcarboxamidoadenosine (NECA)-binding protein from rat brain membranes called P(3) purinoceptor-like protein (P(3)LP), due to its ligand specificity, have not been fully elucidated, we needed a specific ligand to obtain further information about the receptor. We examined the structure-activity relationship (SAR) of various 5'-N-substituted-carboxamidoadenosine derivatives toward P(3)LP and discovered a hydrophobic binding region near the 5'-N-substituted-carboxamide group. From the linear alkyl N-substituted derivatives, the N-n-pentyl derivative 10 was found to be the most potent ligand with a K(i) value of 12 nM. In the series of the N-cycloalkyl derivatives, the N-cyclohexyl derivative 27 was the strongest ligand with a K(i) value of 18 nM. On the other hand, the N-substituents having branched alkyl side chains and bulky cycloalkyl groups did not show any potent affinities for P(3)LP. Therefore, the hydrophobic pocket accommodates approximately a 10-carbon-atom-long linear alkyl side chain, while a considerably stronger hydrophobic binding region of about a 5-carbon-atom-long depth exists near the nitrogen atom of the amide group. This pocket also allows substitution with bulky hydrophobic groups since the 5'-N-cycloalkyl derivatives have high affinities. We also examined the receptor selectivity for the selected nucleosides 10 and 27 with 1 [9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine, HAK2701] and NECA versus P(1) purinoceptor subtypes, such as adenosine A(1), A(2A), A(2B), and A(3) receptors, and found that 27 is the most selective ligand for P(3)LP.

Nucleosides and nucleotides. 122. 2'-C-cyano-2'-deoxy-1-beta-D-arabinofuranosylcytosine and its derivatives. A new class of nucleoside with a broad antitumor spectrum.

Design, synthesis, and tumor cell growth inhibitory effects of 2'-C-cyano-2'-deoxy-1-beta-D-arabinofuranosyl derivatives of cytosine (1i, CNDAC), thymine (6a), uracil (6c), and adenine (6d) have been described. The synthesis of the target compounds was achieved from the corresponding 2'-keto nucleosides 2a-d. Cyanohydrins of 2a-d were converted to thionocarbonates, which were deoxygenated to give the desired 2'-beta-cyano-2'-deoxy derivatives 5a-d, followed by deprotection to furnish the target nucleosides. Of these nucleosides, CNDAC was the most potent inhibitor of cell growth with an IC50 value of 0.53 microM against L1210 cells. In vitro cytotoxicity of CNDAC against human tumor cell lines was also examined; compared with that of 1-beta-D-arabinofuranosylcytosine (ara-C) and 5-fluorouracil (5-FU), CNDAC was more cytotoxic to several cell lines refractory to ara-C. The in vivo effect of CNDAC on M5076 mouse reticulum cell sarcoma was very strong; 99% tumor volume inhibition on day 20 was achieved when it was administrated orally on days 1, 4, 7, 10, 13, and 16 at a dose of 400 mg/kg/day, while 5'-deoxy-5-fluorouridine (5'-DFUR) and 5-FU caused only 50% inhibition at a dose of 500 mg/kg/day and 28% inhibition at a dose of 50 mg/kg/day, respectively, on the same schedule. These results indicated that CNDAC may have potential as a new antineoplastic agent with a broad antitumor spectrum.

Tremorgenic indole alkaloids. Studies directed toward the assembly of the A, F, and I rings of penitrem D: observation of an unexpected stereochemical outcome.

[formula: see text] In this Letter we demonstrate the viability of a highly stereoselective tandem Mannich cyclization-grammine fragmentation/addition cascade, critical for assembly of the A and F rings of penitrem D. We also explored simultaneous execution of this tactic with concurrent construction of ring I. Reinvestigation of a model system provided an explanation for the unanticipated stereochemical outcome at C(28).

Spatial distribution and habitat characterization of anopheline mosquito larvae in Western Kenya.

Studies were conducted to characterize larval habitats of anopheline mosquitoes and to analyze spatial heterogeneity of mosquito species in the Suba District of western Kenya. A total of 128 aquatic habitats containing mosquito larvae were sampled, and 2,209 anopheline and 10,538 culicine larvae were collected. The habitats were characterized based on size, pH, distance to the nearest house and to the shore of Lake Victoria, coverage of canopy, surface debris, algae and emergent plants, turbidity, substrate, and habitat types. Microscopic identification of third- and fourth-instar anopheline larvae did not yield any Anopheles funestus or other anophelines. A total of 829 An. gambiae s.l. larvae from all habitats were analyzed further by rDNA-polymerase chain reaction to identify individual species within the An. gambiae species complex. Overall, An. arabiensis was the predominant species (63.4%), and An. gambiae was less common (31.4%). The species composition of An. gambiae s.l. varied significantly among the sampling sites throughout Suba District. The larval habitats in the southern area of the district had a higher proportion of An. gambiae than in the northern area. Multiple logistic analysis did not detect any significant association between the occurrence of anopheline larvae and habitat variables, and principal component analysis did not identify key environmental factors associated with the abundance of An. gambiae. However, significant spatial heterogeneity in the relative abundance of An. gambiae within the Suba district was detected. When the effect of larval habitat locality was considered in the analysis, we found that the distance to the nearest house and substrate type were significantly associated with the relative abundance of An. gambiae. Future studies integrating detailed water chemistry analysis, remote sensing technology, and the ecology of predators may be required to further elucidate the mechanisms underlying the observed spatial variation of anopheline larval distribution.

An efficient synthesis of cyclic IDP- and cyclic 8-bromo-IDP-carbocyclic-riboses using a modified Hata condensation method to form an intramolecular pyrophosphate linkage as a key step. An entry to a general method for the chemical synthesis of cyclic ADP-ribose analogues

An efficient synthesis of cyclic IDP-carbocyclic-ribose (3) and its 8-bromo derivative 6, as stable mimics of cyclic ADP-ribose, was achieved, and a condensation reaction with phenylthiophosphate-type substrate 15 or 16 to form an intramolecular pyrophosphate linkage was a key step. N-1-Carbocyclic-ribosylinosine derivative 28 and the corresponding 8-bromo congener 24 were prepared via condensation between N-1-(2,4-dinitrophenyl)inosine derivative 17 and a known optically active carbocyclic amine 18. Compounds 24 and 28 were then converted to the corresponding 5"-phosphoryl-5'-phenylthiophosphate derivatives 15 and 16, respectively, which were substrates for the condensation reaction to form an intramolecular pyrophosphate linkage. Treatment of 8-bromo substrate 15 with I2 or AgNO3 in the presence of molecular sieves 3A (MS 3A) in pyridine at room temperature gave the desired cyclic product 12 quantitatively, while the yield was quite low without MS. The similar reaction of 8-unsubstituted substrate 16 gave the corresponding cyclized product 32 in 81% yield. Acidic treatment of these cyclic pyrophosphates 12 and 32 readily gave the targets 6 and 3, respectively. This result suggests that the construction of N-1-substituted hypoxanthine nucleoside structures from N-1-(2,4-dinitrophenyl)inosine derivatives and the intramolecular condensation by activation of the phenylthiophosphate group with I2 or AgNO3/MS 3A combine to provide a very efficient route for the synthesis of analogues of cyclic ADP-ribose such as 3 and 6. Thus, this may be an entry to a general method for synthesizing biologically important cyclic nucleotides of this type.

Anopheline mosquito survival strategies during the dry period in western Kenya.

The dry season survival mechanism of Anopheles gambiae Giles is one of the most vexing deficiencies in our understanding of the biology of the major malaria vectors. In this study, we examined the dynamics of anopheline adult mosquitoes, their larval habitats, and egg survival potential during the dry season in the basin region of Lake Victoria, western Kenya. Through field surveys, we demonstrated two survival strategies of An. gambiae sensu stricto during the dry season: continuous reproduction throughout the year and embryo dormancy in moist soil for at least several days. We further demonstrated that An. gambiae shows a strong preference for moist soil as an oviposition substrate rather than dry soil substrate under the insectary conditions. The observation that anopheline eggs remain a dormant stage to resist desiccation clearly contrasts the conventional wisdom that anopheline eggs hatch shortly after they are laid. Our results from western Kenya are consistent with the suggestion that anopheline mosquitoes do not necessarily suffer a severe population bottleneck during the dry season and thus maintain a large effective population size.

Synthesis and biological activities of cyclic ADP-carbocyclic-ribose and its analogs.

An efficient synthesis of cyclic ADP-carbocyclic-ribose (2), as a stable mimic for cyclic ADP-ribose, was achieved. Treatment of N1-carbocyclic-ribosyladenosine bisphosphate derivative 10 with AgNO3 in the presence of molecular sieves 3A in pyridine gave the desired cyclic product in 93% yield, which was deprotected to give the target cyclic ADP-carbocyclic-ribose (2).

Synthesis of imidazo[4,5-e][1,4]diazepine and 3-substituted 3-deazapurine nucleosides from 1-substituted inosines.

New synthetic methods of imidazo[4,5-e][1,4]diazepine nucleosides 8-11 and 3-substituted 3-deazainosines 14 from inosine have been reported. Treatment of N1-substituted inosines 1-3 with aqueous NaOH gave 5-amino-4-(N-substituted carbamoyl)imidazole ribosides 5-7, followed by appropriate manipulations to afford ring-expanded guanosine, inosine, and xanthosine analogues. Additionally, the 5-amino group of 4-N-allylcarbamoyl derivative 12 was converted into corresponding 5-iodo nucleoside 13. We found that 13 was cyclized to form 3-deaza-3-methylinosine (14) in the presence of Pd catalysts.

Synthesis of sugar-modified 4'-thiocytidine derivatives.

An improved and large-scale synthesis of 1,4-anhydro-2,3,5-tri-O-benzyl-4-thio-D-ribitol (4) has been achieved via dibromination of 2,3,5-tri-O-benzyl-D-ribitol (1). Using the Pummerer reaction, 4'-thiocytidine derivative (10) was successfully prepared in multigram scale. After deprotection of the 2,4-dimethoxybenzoyl group of 10, the resulting 11 was converted into 2'-deoxy-4'-thiocytidine (16) via the radical deoxgenation. The sugar-modified 4'-thiocytidine derivatives, 17 and 18, were also prepared.

Habitat characteristics of Anopheles gambiae s.s. larvae in a Kenyan highland.

Anopheline larval habitats associated with a swamp, were examined in a highland area (1910 m elevation) of western Kenya. A significant association was found between occurrence of Anopheles gambiae Giles s.s. (Diptera: Culicidae) larvae and two factors, habitat size and vegetation type. Over 80% of An. gambiae s.s. larvae were found in small isolated pools, characterized by short plants, occurring in both swamp margins and roadside ditches. However, Anopheles gambiae s.s. was not found in habitats marked by papyrus and floating plants. The larval habitat of An. gambiae s.s. was characterized by warmer daytime temperatures of water, which were significantly affected by habitat size and plant size. The density of indoor resting An. gambiae s.s. was 0.22 per house and negatively associated with distance from the swamp. These results indicate that the practice of swamp cultivation, in populated areas of the African highlands, increases availability and enhances habitat conditions for the malaria vector.

Synthesis and incorporation of tricyclic-imidazo[5',4':4,5]pyrido[2,3-d]pyrimidine nucleosides into oligonucleotides and their thermal stability.

We designed and synthesized four novel tricyclicnucleosides 1-4, which have imidazo[5',4':4,5]pyrido[2,3-d]pyrimidine structures, to construct theramallystable, non-natural, DNA duplexes. Both 1:2 and 3:4 possess four complementary hydrogen-bond pairs and are expected to form more stable base-pairs than the naturally occurring Watson-Crick base-pairs when incorporated into oligodeoxynucleotides (ODNs). NMR studies of these base-pairs at the nucleoside level in CDCl3 identified the expected base-pair formation with four hydrogen bonds. We also synthesized several ODNs containing these nucleosides and measured their thermal stability. We found that if several of the novel base-pairs were incorporated on complementary strands, the resulting DNA duplexes had very high thermal stability.