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A statistical survey of the torsion angles, bond angles, and bond lengths in the sugar and phosphate groups of well-refined mononucleoside, mononucleotide, dinucleoside monophosphate, and trinucleoside diphosphate crystal structures contained in the Cambridge Structural Database and the Nucleic Acid Database is reported. The mean values of the geometrical parameters in these structures and their estimated standard deviations are separated according to their chemistry and conformation. These new parameters serve as a basis for a dictionary of standard nucleic acid geometry.

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Fish oil dietary supplements (FODS) are recommended to increase the intake of polyunsaturated fatty acids (PUFAs), renowned for their beneficial effects on human health. However, FODS also contain anthropogenic contaminants, such as polychlorinated biphenyls and polybrominated diphenyl ethers (PBDEs). Sixty-nine (n=69) PUFA-enriched FODS from 37 producers were collected in 2006 and then analyzed for their levels of organobrominated compounds. Levels of the sum of tri- to hepta-BDEs (BDEs 28, 47, 49, 66, 85, 99, 100, 153, 154, and 183) were typically below 5 ng/g oil, while only a few had higher values of up to 44 ng/g oil. Several peaks in the chromatograms were identified as methoxylated PBDEs (MeO-PBDEs) and polybrominated hexahydroxanthene derivatives (PBHDs). These two groups of compounds have been suggested to be produced by marine organisms (e.g., algae and sponges) and have also been reported in marine samples, such as fish and marine mammals. Median concentrations of MeO-PBDEs and PBHDs (6.2 and 5.3 ng/g oil, respectively) were higher than median concentrations of PBDEs (0.6 ng/g oil), and their maximum values were 1670 and 200 ng/g oil, respectively. FODS are intended to be consumed on a daily basis, and the median daily intakes of MeO-PBDEs and PBHDs from FODS were 3 and 6 times higher than the median intake of PBDEs (3 ng/day). Consumption of FODS does not appear to substantially increase the total dietary intake of PBDEs since the median daily intake

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What are the future directions of the field of nucleic acid crystallography? Although there have been many duplex structures determined, the sample is still relatively small. This is especially true if one wants to derive enough information about the relationships between sequence and structure. Indeed, there are data for all the possible 10 dimer steps, but for some steps it is very limited. If the structural code resides in trimers or tetrad steps then there is simply not enough data to do meaningful statistical analyses. So the first direction that needs to be explored is the determination of more structures with more varied sequences. The other noticeable thing about the data is the shortness of the strands. While it is probably true that attempts to crystallize very long sequences will not meet with success, the idea of crystallizing sequences engineered to fit together via sticky ends such as has been done for the CAP-DNA complex (Schultz et al., 1990) should give data about the behavior of much longer stretches of DNA. The question of the effects of environment on the structure of DNA continues to be a very important one to address since DNA is rarely alone. The preliminary data we have analysed from the current sample shows that the conformation of some steps are very sensitive to packing type. Numerous studies of the hydration around DNA shows that there is a real synergy between the hydration structure and the base conformation. More data will allow further quantitation of these observations. RNA structure is the next very exciting frontier. The emerging structures of duplexes with internal loops, the two hammerhead ribozyme structures and the group I intron ribozyme have given us a glimpse of the complexity and elegance of this class of molecules. With the technology now in place to allow the determination of the structures of these molecules, the expectation is that now we will see a large increase in the number of these structures in the NDB.

Synthesis of Novel Quinolone‐Chemotherapeutics. V. Methodical Investigations on the Synthesis of Quinolone Chemotherapeutics. The synthesis of 6, 7‐dihalogen‐N‐ethyl‐4‐oxo‐l, 4‐dihydroquinoline‐3‐carboxylic acids (3a, b) from 3, 4‐dihalogen‐anilines is a three‐step processes: (a) N‐ethylation, (b) reaction with ortho formic ester and Meldrum's acid, (c) intramolecular cyclization. An increase of the total yields in comparison with known methods is mainly connected with the third step. Here the Meldrum's method allows reactions in solution at temperatures ≥ 100°C. With application of special Lewis acids the 6, 7‐dihalogen‐substituted products are formed in relatively high yields (6, 7‐difluoro‐l‐ethyl‐4‐oxo‐1, ‐4‐dihydro‐quinoline‐3‐carboxylic acia (3a): 71%; 7‐chloro‐6‐fluoro‐1 ‐ethyl‐4‐oxo‐1, 4‐dihydro quinoline‐3‐carboxylic acid (3b): 60%) without impurities of the corresponding 5, 6‐dihalogen substituted isomers. Anhydrides (5) of 4‐oxo‐1, 4‐dihydro‐quinolone‐3‐carboxylic acids with dibromo and difluoro‐boric acid were synthesized and shown to facilitate the aromatic nucleophilic substitution. The kinetics of two reactions (5a → 6 and 3b → 7) were determined and relative reaction rates established.

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