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15_Biochemistry Test Notes


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Unformatted text preview: Hemiacetal & hemiketal formation H , An aldehyde can I l . = sQ'—, _-.__ V_ .. reactwrthan O + OH —b P C (I: 0“ alcohol to form . R a hemiacetal. aldehyde alcohol hemiacetal A ketone can 3 T react with an c=o + "R—GH —o ‘R—J—C—OH alcohol to form Fli‘ '1'}. a hemiketal. kelone alcohol hemiketal Ecitizen HGrC—H 'I Home? H'—E(|:—OH : H H—C—OH H -. ‘ | OH ,_CH,0H D-fiuctose(linear) a—D-fiuctoturanose Fructose forms either ' a 6 member pyranose ring, by reaction of the C2 keto group with theOH on C6, or e a 5- member furanose nng, by reaction of the C2 keto group‘with the OH on C5. u-D-glucopyranose B—D—glucopymnose . Because of the tetrahedral nature of carbon bonds, pyranose sugars actuallyassu’r'n‘e'a "chair" o'r'"boat"‘ configuration, depending on the sugar. The representation above reflects the chair configuration of the glucopyranose ring more accurately than the Haworth projection. Pentoses and hexoses can cyclize as the ketone or aldehyde reacts with a distal OH. , Glucose forms an intra—molecular . hemiacaal, asvthe _.CH2°H o ' Cl aldehyde . & ”Il/Hl . C5 OH react, to ’ fl" '4‘ form a (w-member 0“ . , pyranose ring, H on named after pyran. “whims: {topmost- Those representations of the cyclic sugirs are called Haworth projections. Hawortfi‘ projections represent the cyclic sugars as having essentially planar rings, with theOH at the anomeric C1: 0 01 (OH below the ring) ' 1% (OH above the ring). Glycosidic Bonds The anomeric hydroxyl and a hydroxyl of another sugar or some other compound can join together, splitting out water to form a glycosidic bond: R-OH + HO-R' 9 R-O-R' + H20 E. g., methanol reacts with the anomeric OH on glucose to form nnethyl glucoside (methyl-glucopyranose) 'Q*OH I .. .t CH +420 ,A HO . H + erg-0H 1., Ho H H OCH, . u-D-glucopymose methanol methyla~D—glucopymnose _ ...
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