CHEM1907/ J-7 June 2003 B CHO. Give the products obtained when D-xylose is treated with the following reagents. [Ag(NH 3 ) 2 ] + / OH solution

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1 EM1907/ J-7 June 2003 onsider the following two monosaccharides, (A) and (B). 8 2 (A) 2 (B) -D-altropyranose -D-xylofuranose Draw Fischer projections of the open chain forms of A and B. A B 2 2 Give the products obtained when D-xylose is treated with the following reagents. [Ag( 3 ) 2 ] + / solution 2 ab 4 in methanol solvent Draw the aworth structure of a non-reducing disaccharide, which yields D-altrose and D-xylose on acid hydrolysis. 2 2

2 EM1907/ J-7 June 2003

3 EM1907/ J-8 June 2003 The side-chain of the amino acid tryptophan () is a substituted derivative of the heterocycle indole (D). Explain with the aid of diagrams whether you would expect indole to have aromatic stability or not. Would you expect the nitrogen atom of indole to be basic? Give reasons for your answer () (D) Indole is aromatic because: it is a fused ring system with all rings co-planar all atoms in the rings are sp 2 hybridised with p-orbitals perpendicular to the ring it has 10 π electrons, which obeys the (4n + 2) rule required for aromaticity. Indole is not basic as the "lone pair" on the nitrogen is is part of the aromatic π system and thus not free to react. ydrolysis of damp (E), a nucleotide important in DA synthesis, gives the sugar D-2-deoxyribose and the nucleic base adenine. Give the structure of adenine and the structure of one tautomer of adenine. 2 2 P (E) adenine tautomer of adenine 2 2

4 EM1907/ J-9 June 2003 onsider the tripeptide phenylalanylglutamyltyrosine (Phe-Glu-Tyr) (F), whose constitutional formula is shown below. 9 (F) Draw the constitutional formula(s) of the product(s) obtained when the tripeptide is subjected to the following conditions. cold 2 M a M l / heat The pk a values of tyrosine are pk a1 = 2.20 ( -), pk a2 = 9.11 ( - 3 ) and pk a3 = ( ). Draw the structure of the zwitterionic form of tyrosine. 2 3 ASWER TIUES TE EXT PAGE

5 EM1907/ J-9 June 2003 At what p will this be the predominant species in aqueous solution? 5.66 Give the constitutional formulas for the following dipeptides present in water solution at the indicated p values. Tyr-Phe, p 12.0 Glu-Tyr, p

6 EM1907/EM J-11 June 2004 onsider the tripeptide L-lysyl-L-glutamyl-L-tyrosine (Lys-Glu-Tyr), (F), whose constitutional formula is shown below. 8 (F) ( 2 ) Draw the Fischer projections with L-configurations for the amino acids (in their correct ionisation states) obtained from the hydrolysis of (F) using hot concentrated l solution ( 2 ) The pk a values of lysine are pk a1 = 2.18 ( -), pk a2 = 8.95 ( - 3 ) and pk a3 = (-( 2 ) 4 3 ). Draw the structure of the zwitterionic form of lysine. 2 2 ( 2 ) 4 3 At what p will this be the predominant species in aqueous solution? 9.74 ASWER TIUES TE EXT PAGE

7 EM1907/EM J-11 June 2004 Give the constitutional formulas for the following dipeptides present in water solution at the indicated p values. Glu-Tyr, p 12.0 Glu-Lys, p ( 2 )

8 EM1907/EM J-8 June 2004 Lactose, 4--( -D-galactopyranosyl)- -D-glucopyranose is the major sugar in human and cow's milk Lactose Does lactose display mutarotation? Justify you answer. Yes. The right hand ring contains the hemiacetal functional group as the α- anomer. It therefore equilibrates with the open chain (aldehyde + alcohol) form and the β-anomer. Draw the Fischer projection of the open chain form of D-galactose. 2 Give the products obtained when D-galactose is treated with the following reagents. methanol / / heat [Ag( 3 ) 2 ] / solution

9 EM1907/EM J-9 June 2004 Acid hydrolysis of a non-reducing disaccharide yields D-galactose as the only product. Draw the aworth structure of one such disaccharide ow many different disaccharides are possible in the preceding question? What is the relationship between these compounds? 3 disaccharides possible. (The possible linkages are α-α, α-β and β-β. The β-α is identcal to the α-β.) They are all diastereoisomers of each other. TE REMAIDER F TIS PAGE IS FR RUG WRKIG LY

10 EM1907/ J-10 June 2005 Give the products obtained when lysine is treated with the following reagents. excess methanol / l dilute a ( 2 ) 4 3 ( 2 )

11 EM1907/ J-7 June 2005 onsider the structures of the two aldohexoses shown below (A) (B) -D-allopyranose -D-altropyranose (A) Draw the Fischer projection of the open chain forms of sugars (A) and (B). (B) 2 2 Give the products obtained when D-allose is treated with the following reagents. acidified methanol ab 4 in methanol solvent In the case of the product obtained from the reaction with ab 4 in methanol, specify the optical rotation as "(+)", "( )", "zero" or "cannot be predicted". Justify your choice. Zero. It is a meso compound and is therefore achiral and optically inactive. TIS QUESTI IS TIUED TE EXT PAGE.

12 EM1907/ J-8 June 2005 Draw the aworth structure of -D-allopyranosyl- -D-altropyranoside Will this disaccharide be a reducing sugar? Explain your answer. o, not a reducing sugar. o hemiacetal functional group in equilibrium with open chain aldehyde. TE REMAIDER F TIS PAGE IS FR RUG WRKIG LY

13 EM1907/ J-9 June 2005 onsider the three amino acids shown below ( 2 ) threonine (Thr) aspartic acid (Asp) lysine (Lys) Draw the constitutional formulas for the following dipeptides present in water solution at the indicated p values. Thr-Lys, p 1.0 Asp-Thr, p ( 2 ) Draw the stereoformula for L-threonine and indicate its absolute configuration using the (R)- and (S)- convention. b 2 2 a c 2 3 Absolute configuration (S) L-threonine The pk a values of aspartic acid are 1.88 ( -), 9.60 ( - 3 ) and 3.65 (- 2 ). Draw the zwitterionic form of aspartic acid At what p will this be the predominant species in aqueous solution? 2.77