10.1016/j.tet.2009.04.048
The research describes a novel method for synthesizing pentoses, which are five-carbon sugars with significant applications in pharmaceuticals and cosmetics, particularly as building blocks for nucleoside analogues in antiviral and antitumoral therapies. The study's purpose is to develop an efficient de novo synthesis route for pentoses, starting from (Z)-2-buten-1,4-diol and using cyanohydrins as key intermediates. The key steps involve an enzyme-catalyzed enantioselective HCN addition to O-protected 4-hydroxybut-2-enal using hydroxynitrile lyase from Hevea brasiliensis, followed by an asymmetric dihydroxylation. The researchers investigated the influence of the double bond configuration and protecting groups on the reaction's conversion and selectivity. The study concludes that the configuration of the double bond and the protecting group significantly impact the reaction's efficiency and selectivity. Only the allyl-protected compound was found to be sufficiently selective for the synthesis of pentoses. The dihydroxylation step was also influenced by the protecting group at position 4, yielding different ratios of D-arabinose and L-ribose. Key chemicals used in the research include (Z)-2-buten-1,4-diol, various protecting groups such as allyl, benzyl, methoxymethyl, t-butyldimethylsilyl, and t-butyldiphenylsilyl, hydrocyanic acid (HCN), and the enzyme hydroxynitrile lyase. The findings provide valuable insights into the synthesis of pentoses and highlight the importance of protecting group selection in achieving high enantiomeric purity and desired product ratios.
10.1016/S0957-4166(97)00178-X
The research investigates the catalytic enantioselective addition of hydrogen cyanide to benzaldehyde and p-methoxybenzaldehyde using cyclo-dipeptides based on His and the unnatural (αMe)Phe as catalysts. The LL dipeptide, specifically cyclo-[L-His-L-(αMe)Phe] (15), is a key catalyst in the study. It is a cyclic dipeptide composed of L-histidine (His) and L-(α-methyl)phenylalanine ((αMe)Phe). This compound is synthesized through a series of chemical reactions starting from L-(αMe)Phe and L-histidine, involving protection, coupling, and cyclization steps. The LL dipeptide 15 is notable for its conformational rigidity, which is attributed to the incorporation of the unnatural (αMe)Phe residue. This rigidity is crucial for its catalytic activity in the enantioselective addition of hydrogen cyanide to benzaldehyde and p-methoxybenzaldehyde. The study demonstrates that 15 achieves high enantiomeric excesses (up to 99% e.e. for benzaldehyde and 89% e.e. for p-methoxybenzaldehyde derivatives) at low temperatures (-40°C) with excellent yields (98% and 93%, respectively). NMR studies suggest that the orientation of the aldehyde in the reaction complex with 15 is different from the Tanaka model, with the aldehyde hydrogen-bonded to the NH of the (αMe)Phe residue rather than the histidine residue.
10.1021/jp962686g
The research investigates the reactions of the cyanomethylene (HCCN) radical with nitric oxide (NO) and molecular oxygen (O2) at 298 K using infrared kinetic spectroscopy. The study determines the overall second-order rate constants for these reactions as (3.5 ± 0.6) × 10^-11 cm3 molecule^-1 s^-1 for HCCN + NO and (1.8 ± 0.4) × 10^-12 cm3 molecule^-1 s^-1 for HCCN + O2. For the reaction with NO, hydrogen cyanide (HCN) and fulminic acid (HCNO) were observed as products, while for the reaction with O2, HCN, hydrogen isocyanide (HNC), and carbon dioxide (CO2) were identified. The study also searched for but did not detect several other potential products, including isocyanic acid (HNCO), cyanic acid (HOCN), formyl radical (HCO), isofulminic acid (HONC), hydroxyl radical (OH), and ethynyl radical (C2H). The research concludes that the observed products are likely formed through secondary processes rather than directly from the reactions of HCCN with NO or O2.
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F+,
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