Passage
The protozoan Euglena gracilis expresses glycosyltransferases (enzymes that add carbohydrates to molecules) and glycosidases (enzymes that remove carbohydrates) within its membrane. These enzymes were previously studied using radiolabeled sugars. To avoid the use of radioactive materials, fluorescence-based assays were investigated. Derivatives of the fluorescent molecule coumarin were attached to carbohydrates (Figure 1) for detection in fluorescence assays.Compound 1, a carbohydrate derivative with hydroxyl groups protected by benzoate (Bz) , reacted with Compound 2 to form Compound 3. ¹³C NMR confirmed the formation of Compound 3 by observing a distinct C-H coupling at the anomeric carbon. Hydroxyl deprotection and addition of Compound 4 (a coumarin analogue) gave Compound 5, a fluorescent coumarin derivative. Compound 6, another coumarin derivative, was made following a similar sequence except an additional sugar was attached before the addition of the coumarin group.
Figure 1 Synthesis of fluorescent coumarin derivatives (Note: HCT denotes the fluorescent butyl hydroxycoumarin triazole group.) Small vesicles called microsomes were isolated from Euglena gracilis membranes, and microsomal glycosyltransferase activities were investigated using a hexose donor substrate and either Compound 5 (Figure 2) or Compound 6 (Figure 3) as the acceptor substrate. Thin-layer chromatography (TLC) analysis indicated the formation of a new product in each assay. These products were purified and characterized by liquid chromatography-mass spectrometry (LC-MS) . The molecular ion for each product was subjected to another round of MS, in which individual hexose units (MW) = 162) were cleaved from the coumarin derivatives that were formed during the assay. The MW of hydroxycoumarin triazole (HCT) is 301.
Figure 2 Analysis of Compound 5 as the acceptor substrate: (A) TLC analysis of fluorescent products; (B) Mass spectrum of product A fragmented molecular ion peak
Figure 3 Analysis of Compound 6 as the acceptor substrate: (A) TLC analysis of fluorescent products; (B) Mass spectrum of product B fragmented molecular ion peak
Adapted from: I. M. Ivanova et al., "Fluorescent mannosides serve as acceptor substrates for glycosyltransferase and sugar-1-phosphate transferase activities in Euglena gracilis membranes." Carbohydrate Research. © 2017 Elsevier.
-If researchers needed to synthesize Compound 1 before beginning the synthesis of Compound 5, which of the following sugars would require the fewest steps if used as a starting material?

Question

Passage
The protozoan Euglena gracilis expresses glycosyltransferases (enzymes that add carbohydrates to molecules) and glycosidases (enzymes that remove carbohydrates) within its membrane. These enzymes were previously studied using radiolabeled sugars. To avoid the use of radioactive materials, fluorescence-based assays were investigated. Derivatives of the fluorescent molecule coumarin were attached to carbohydrates (Figure 1) for detection in fluorescence assays.Compound 1, a carbohydrate derivative with hydroxyl groups protected by benzoate (Bz) , reacted with Compound 2 to form Compound 3. ¹³C NMR confirmed the formation of Compound 3 by observing a distinct C-H coupling at the anomeric carbon. Hydroxyl deprotection and addition of Compound 4 (a coumarin analogue) gave Compound 5, a fluorescent coumarin derivative. Compound 6, another coumarin derivative, was made following a similar sequence except an additional sugar was attached before the addition of the coumarin group.

Figure 1 Synthesis of fluorescent coumarin derivatives (Note: HCT denotes the fluorescent butyl hydroxycoumarin triazole group.) Small vesicles called microsomes were isolated from Euglena gracilis membranes, and microsomal glycosyltransferase activities were investigated using a hexose donor substrate and either Compound 5 (Figure 2) or Compound 6 (Figure 3) as the acceptor substrate. Thin-layer chromatography (TLC) analysis indicated the formation of a new product in each assay. These products were purified and characterized by liquid chromatography-mass spectrometry (LC-MS) . The molecular ion for each product was subjected to another round of MS, in which individual hexose units (MW) = 162) were cleaved from the coumarin derivatives that were formed during the assay. The MW of hydroxycoumarin triazole (HCT) is 301.

Figure 2 Analysis of Compound 5 as the acceptor substrate: (A) TLC analysis of fluorescent products; (B) Mass spectrum of product A fragmented molecular ion peak

Figure 3 Analysis of Compound 6 as the acceptor substrate: (A) TLC analysis of fluorescent products; (B) Mass spectrum of product B fragmented molecular ion peak
Adapted from: I. M. Ivanova et al., "Fluorescent mannosides serve as acceptor substrates for glycosyltransferase and sugar-1-phosphate transferase activities in Euglena gracilis membranes." Carbohydrate Research. © 2017 Elsevier.
-If researchers needed to synthesize Compound 1 before beginning the synthesis of Compound 5, which of the following sugars would require the fewest steps if used as a starting material?

Quizplus · Accepted Answer

11ecba2d_12ad_622f_a3bf_ef9dba531e17_MD0008_00 Sugars can be classified in several ways, including by the stereochemistry of the sugar, the number of carbons in the sugar, the number of carbohydrate units in the molecule, and the functional groups present in the sugar. Some of the most common monosaccharides include ribose, glucose, fructose, mannose, and galactose. Compound 1 contains six carbons and one of the C-1 substituents is a hydrogen atom, indicating that Compound 1 is derived from a hemiacetal and, more specifically, from a six-carbon aldose. In the orientation shown in Figure 1, the substituents on C-2 and C-3 are both above the plane of the ring and the C-4 substituent is below the plane. These characteristics of Compound 1 match those of mannose, which has its hydroxyl substituents in the same orientation. Therefore, mannose can be used to synthesize Compound 1. (Choice A) Fructose is a six-carbon ketose with the anomeric carbon at C-2. Compound 1 is derived from an aldose with the anomeric carbon at C-1. (Choice B) Ribose contains only five carbons, and Compound 1 is derived from a six-carbon sugar. (Choice D) Glucose differs from Compound 1 in the orientation of the substituent at C-2. Glucose and mannose are epimers. Educational objective: Sugars are classified in a number of ways including by their stereochemistry, the number of carbons in the sugar, the number of sugar units in the molecule, and the type of functional group present in the sugar. Sugars that are prevalent in nature are known by their common names (ie, ribose, glucose, fructose, mannose, galactose).

Passage The Protozoan Euglena Gracilis Expresses Glycosyltransferases (Enzymes That Add Carbohydrates