Concept explainers
The example of a silyl–Hilbert–Johnson nucleosidation reaction in Section 25.3 is presumed to involve an intermediate ribosyl cation that is stabilized by intramolecular interactions involving the C2 benzoyl group. This intermediate blocks attack by the heterocyclic base from the
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- Draw the dinucleotide dApdG (shown above). Draw a dinucleotide that you would expect to hydrogen bond most stably to dApdG. Include every atom and every ring atom number, every charge, correct orientation of the base and the backbone linkages with respect to the ribose ring, the number of angstroms between N’s and O’s involved in the hydrogen bonds, and the number of angstroms between the riboses involved as support for each base in the hydrogen bonded pair.arrow_forwardThe enzyme that catalyzes the C-Cg bond cleavage reaction that converts serine to glycine removes the substituent (R) bonded to the a-carbon in the first step of the reaction. Starting with PLP bound to serine in an imine linkage, propose a mechanism for this reaction. (Hint: The first step involves removal of the proton from serine's OH group.)arrow_forward5-Bromouracil (BU) resembles thymine sufficiently that BU base-pairs readily with adenine in a DNA helix, and it can readily substitute for thy- mine in DNA replication. However, its electron distribution allows it to resemble cytosine sufficiently that BU can pair with guanine. Show how a few rounds of replication in the presence of BU could convert an A-T base pair to G-C, and identify the products of each round of replication.arrow_forward
- Under acidic conditions (catalytic amount of acid) in anhydrous methanol, D-galactose can be converted to the methyl galactopyranoside X on the right side of the reaction arrow. Write a detailed mechanism for the reaction. OH H+ HO HO `Me MeOH HO 'OH HO "OH OH OH Xarrow_forwardPlease give the resulting product of the reaction between ribose sugar and the fluorinated pyrimidine (denoted by a starred reactive nitrogen). What type of starting sugar is this ? α (Alpha) or β (beta)arrow_forwardResearchers analysed a glycopeptide (a peptide carrying one or several oligosaccharide groups) and determined both the sequence of the peptide and the sequence of the sugar molecule. The latter was identified as a diholoside coupled to the peptide by an osidic bond. The systematic name of this sugar is: B-D-glucopyranosyl-(1→4)-ß-D-galactopyranose. : Represent the chemical formula of this diholoside in a way that all oses are Question 1 represented according to the Haworth convention. Apart from the furane and/or pyrane cycles all atoms of this molecule must be given.arrow_forward
- Of the four DNA bases, why is guanine most likely to be modified after exposure to polycyclic hydrocarbons such as benzo(a)pyrene, as shown in Figure ? (Hint: Consider the pKa values of the four DNA bases.)arrow_forwardDraw a diagram of the linear and ring structures of ribose. Show the biochemical mechanism of cyclization of each and name the resultant ring – including the ring type & anomeric carbon designation. Draw and name an amine version, reduced version, and oxidized version, either in ring or Fisher projection.arrow_forwardWhat does the "alpha" indicate in "α-D-ribofuranose"? It is the first anomeric form. The sugar is "right-handed." It is the dominant form of the possible forms of D-ribofuranose. The position of the C1 -OH group relative to the plane of the ring. None of these.arrow_forward
- An important technique for establishing relative configurations among isomeric aldoses and ketoses is to convert both terminal carbon atoms to the same functional group. This can be done either by selective oxidation or reduction. As a specific example, nitric acid oxidation of d-erythrose gives meso-tartaric acid . Similar oxidation of d-threose gives (2S,3S)-tartaric acid. Given this information and the fact that d-erythrose and d-threose are diastereomers, draw Fischer projections for d-erythrose and d-threose. Check your answers against Table 25.1.arrow_forwardShow the steps and products of the Haworth Projection structure of the following saccharides. The males have to work on the naturally occurring form of D-ribose and the females are the structure of D-mannose. Expanded structure of the given molecule Fischer Projection HAWORTH PROJECTIONarrow_forwardA Cu² reagent called Benedict's reagent in the presence of a base is commonly used to oxidize an aldose to the aldonic acid. Carbohydrates that are oxidized with Benedict's reagent are called reducing sugars because the Cu (blue color) in Benedict's reagent is reduced to Cu (brick-red) during the reaction. What product is formed when D-sorbose is treated with Benedict's reagent? Change the structure in the drawing area to show the aldonic acid product formed if the compound is easily oxidized. If there are no changes to be made, check the No changes box under the drawing area. H- HO- H- CH₂OH C=0 OH -H OH CH₂OH X 0:0 #arrow_forward
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