Sugars are carbohydrates, that is, molecules usually with the empirical formula C(H2O), and structural formulas made up of polyhydroxy aldehydes or ketones. Because of their polyfunctional nature, sugars can undergo a wide variety of transformations upon treatment with acids, bases, or heat, and upon reaction with other simple reagents and enzymes. While many sugars occur in nature and are thus readily available, the synthesis and modification of simple sugars is a necessary step in studies of enzymatic processes.Higher sugars can be synthesized from the simple carbohydrate D-glyceraldehyde with the following procedure:D-glyceraldehyde (Compound A) is reacted with HCN to produce a cyanohydrin (Compound B). Compound B is then treated with hydrogen gas and a modified palladium catalyst (similar to the Lindlar reagent) to give Compound C. Compound C is hydrolyzed to give the higher sugars in Mixture D. This reaction is summarized in Figure 1. Mixture D contains two compounds, which can be separated by crystallization. Two doublets near 9.5 (, ppm) are observed in the 1H NMR spectrum of mixture D, with each doublet corresponding to one of the two products present in the mixture. IR spectroscopy shows broad absorptions for both products around 3300 cm1. The hydroxyl groups of carbohydrates can also participate in reactions. For example, D-glyceraldehyde can react with chloromethane under basic conditions to yield a completely methylated product. This SN2 reaction is shown in Figure 2.Figure 2 Methylation of D-glyceraldehydeThe two sugars in Mixture D are:
Answer(s): C
Epimers are sugars that differ in the configuration about a single stereocenter. A new chiral center is formed in the first step of the sugar extension (cyanohydrin formation). This will lead to the formation of two different sugars in Mixture D. Choice A because enantiomers are mirror images that differ in configuration at every stereocenter. As shown above, these epimers differ at a single stereocenter.Choice B is incorrect because anomers aresugars that differ in their configuration about the new stereocenter formed when they adopt a ring configuration. The sugars shown above would generally not form rings because of the ring strain of 4-membered rings.Choice D is incorrect because dissaccharides are formed from the condensation of two monosaccharides (like the ones in mixture D).
Sugars are carbohydrates, that is, molecules usually with the empirical formula C(H2O), and structural formulas made up of polyhydroxy aldehydes or ketones. Because of their polyfunctional nature, sugars can undergo a wide variety of transformations upon treatment with acids, bases, or heat, and upon reaction with other simple reagents and enzymes. While many sugars occur in nature and are thus readily available, the synthesis and modification of simple sugars is a necessary step in studies of enzymatic processes.Higher sugars can be synthesized from the simple carbohydrate D-glyceraldehyde with the following procedure:D-glyceraldehyde (Compound A) is reacted with HCN to produce a cyanohydrin (Compound B). Compound B is then treated with hydrogen gas and a modified palladium catalyst (similar to the Lindlar reagent) to give Compound C. Compound C is hydrolyzed to give the higher sugars in Mixture D. This reaction is summarized in Figure 1. Mixture D contains two compounds, which can be separated by crystallization. Two doublets near 9.5 (, ppm) are observed in the 1H NMR spectrum of mixture D, with each doublet corresponding to one of the two products present in the mixture. IR spectroscopy shows broad absorptions for both products around 3300 cm1. The hydroxyl groups of carbohydrates can also participate in reactions. For example, D-glyceraldehyde can react with chloromethane under basic conditions to yield a completely methylated product. This SN2 reaction is shown in Figure 2.Figure 2 Methylation of D-glyceraldehydeWhat are the missing compounds, respectively, in the following reaction?
Answer(s): D
This reaction is called the Wolff-Kishner Reduction and reduces a carbonyl group to the corresponding alkane.The first step, reaction with hydrazine, leads to the formation of a hydrazone. The second step occurs in basic solution and leads to the evolution of nitrogen gas and the formation of the corresponding hydrocarbon.Choice A is incorrect because the indicated structures do not form.Choice B is incorrect because ethers do not form alkoxides under basic conditions. Ethers are relatively unreactive.Choice C is incorrect because hydrazine reacts with a carbonyl to form hydrazone. This is a condensation reaction, not an addition reaction, and the addition product shown would not form.
Sugars are carbohydrates, that is, molecules usually with the empirical formula C(H2O), and structural formulas made up of polyhydroxy aldehydes or ketones. Because of their polyfunctional nature, sugars can undergo a wide variety of transformations upon treatment with acids, bases, or heat, and upon reaction with other simple reagents and enzymes. While many sugars occur in nature and are thus readily available, the synthesis and modification of simple sugars is a necessary step in studies of enzymatic processes.Higher sugars can be synthesized from the simple carbohydrate D-glyceraldehyde with the following procedure:D-glyceraldehyde (Compound A) is reacted with HCN to produce a cyanohydrin (Compound B). Compound B is then treated with hydrogen gas and a modified palladium catalyst (similar to the Lindlar reagent) to give Compound C. Compound C is hydrolyzed to give the higher sugars in Mixture D. This reaction is summarized in Figure 1. Mixture D contains two compounds, which can be separated by crystallization. Two doublets near 9.5 (, ppm) are observed in the 1H NMR spectrum of mixture D, with each doublet corresponding to one of the two products present in the mixture. IR spectroscopy shows broad absorptions for both products around 3300 cm1.The hydroxyl groups of carbohydrates can also participate in reactions. For example, D-glyceraldehyde can react with chloromethane under basic conditions to yield a completely methylated product. This SN2 reaction is shown in Figure 2.Figure 2 Methylation of D-glyceraldehydeIn glucose, the carbonyl carbon can be attacked, intramolecularly, by the hydroxyl oxygen of carbon-5 to form:
Answer(s): B
A hemiacetal is formed through reaction of a carbonyl group and a hydroxyl group. In this question, these two groups occur on the same molecule of glucose.Choice A is incorrect because glucofuranose is the five-membered ring that is formed through attack by the hydroxyl oxygen of carbon-4, not carbon-5 as the question stem states. Furanose refers to a five-membered ring while pyranose refers to the more energetically favorable six-membered ring.Choice C is incorrect because a lactone is a cyclic ester. No ester linkage is formed in this case.Choice D is incorrect because a glycoside is a sugar acetal. These acetals are formed during polysaccharide formation. They can also be formed by exposing a sugar like D-glucose to another alcohol in an acidic environment.
Before birth, the rodent brain is sexually undifferentiated. It is only in the first few days following birth, during a period referred to as the critical period, that the rodent brain differentiates along male or female lines. The hormone testosterone plays a critical role in this development. Specifically, sexual differentiation is determined by the presence of estradiol, an estrogen derivative of testosterone, in certain areas of the brain. Testosterone is converted to estradiol in critical brain cells that contain the enzyme aromatase.To study the effects of testosterone on the neonatal rodent brain, the following experiments were conducted: The above research, combined with additional studies, concluded that testosterone has two "organizational" effects on the male rodent brain:DefeminizationModerate levels of testosterone-derived estradiol during the critical period are sufficient for defeminization of the brain. Defeminization of the rodent brain results in loss of estrogen positive feedback on LH and FSH secretion and the ensuing loss of cyclicity, as well as loss of female sex behavior.MasculinizationHigh levels of estradiol due to high levels of testosterone during the critical period results in masculinization of the brain. Masculinization leads to the induction of male sex behavior including antagonism towards other males and the mounting of females.A mutant male neonatal rodent with a defective aromatase enzyme is injected with large doses of testosterone during the critical period. Which of the following would occur?
The passage states that aromatase converts testosterone to estradiol. Estradiol that has been derived from testosterone leads to defeminization (loss of cyclicity and female sex behavior) and masculinization (induction of male sex behavior) of the rodent brain. If aromatase is defective, no estradiol will be produced even when large doses of testosterone are present. Thus, the brain will develop along female lines. Results of this situation are similar to those of experiment 1 in which the rodent is castrated and therefore has no source of testosterone.Choices A, C, and D are all incorrect because these effects are caused by estradiol in the brain. Without aromatase, there will be no estradiol in the male rodent brain.
Before birth, the rodent brain is sexually undifferentiated. It is only in the first few days following birth, during a period referred to as the critical period, that the rodent brain differentiates along male or female lines. The hormone testosterone plays a critical role in this development. Specifically, sexual differentiation is determined by the presence of estradiol, an estrogen derivative of testosterone, in certain areas of the brain. Testosterone is converted to estradiol in critical brain cells that contain the enzyme aromatase.To study the effects of testosterone on the neonatal rodent brain, the following experiments were conducted:The above research, combined with additional studies, concluded that testosterone has two "organizational" effects on the male rodent brain:DefeminizationModerate levels of testosterone-derived estradiol during the critical period are sufficient for defeminization of the brain. Defeminization of the rodent brain results in loss of estrogen positive feedback on LH and FSH secretion and the ensuing loss of cyclicity, as well as loss of female sex behavior.MasculinizationHigh levels of estradiol due to high levels of testosterone during the critical period results in masculinization of the brain. Masculinization leads to the induction of male sex behavior including antagonism towards other males and the mounting of females.The conversion of testosterone to estradiol is what type of reaction?
The passage states that the conversion of testosterone to estradiol is catalyzed by aromatase. In this reaction, an aromatic ring is formed. Thus, it is an aromatization reaction.Choice A is incorrect because a reduction involves addition of hydrogens to a molecule. In this case, hydrogens are removed. A pair of hydrogens is removed from the ring and the resulting cyclic dienone tautomerizes to its enol form.Choice C is incorrect because electrophilic aromatic substitution is substitution on an aromatic ring. This reaction did not begin with an aromatic ring.Choice D is incorrect because (Friedel-Crafts) alkylation requires an aromatic ring (it is an electrophilic substitution reaction).
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