Reactivity of carbohydrates Hemiacetalstttemiketals Aldehyde ketone carbons are electrophilic Alcohol oxygen atom is nucleophilic Aldehydes attacked by alcohols Hemlacetais ketones attacked by alcohols Hemiketals Basis of cyclization of sugars Cyclization of Monosaccharides ketone R Cy Aldehyde 1 1 10 R2 R 0B OH H Alcohol Hemiacetal HO RS R OR3 Rtd OR HOH 14 Acetal Rt C o 140 R R g OR3 RL R3 HOH Ho R FH 2 R2 R2 R Alcohol Hemiketal Keta 1 Nucleophilic alcohol attacks electrophilic carbonyl carbon allows formation Ofahemlacetal D Glucose 2 linear carbs forma ring structure chair forms of B Dglucopyranose 3 At completion carbonyl carbon is reduced 10 an alcohol orientation of alcohol around carbon is variable and transient Pentoses hexoses readily undergo intramolecular cyclization former carbonyl carbon becomes achiral center anomeric carbon Position determines lftheancmterlsa B Hydroxyl group on the opposite side trans 0f he ring as CHZOH moiety configuration Isai Hydroxyl group on the same side Cis ofthe nngasctl CH moiety configuration SB 9 14 Hac CH Pyran HC CH c c H H Furan Axis CHZOH OH o Axis H ki i H G OH 10 34 1 1 H OH 1 1 54 OH GCHZOH 1 GCHZOH OH 1 1 H HAP i a 4 OH 2 HZOH f 1 4 1191 1 24 IF Ci H OH 3 GCHZOH 1T 4C 1101 1 1 1 31 H 21 OH a D Ghlcopyranose B DG ucopyranose cyclohexane rings chair boat conformations Pyranose rings chair conformations Multiple chair conformations possible require energy for interconversion 46kg mole pypanoses and Futanoses six membered oxygen containing rings pyranoseslpyranring structure five membered oxygen containing rings furanoseslfuranring Structure anomeric carbon usually drawn on the right side Hexoses Derivatives Glucose fam s CHZOH CHZOH 1041 no I i H H MHz F NH 0 B D Glucosamine N acetyl B glucosamine B D Glucose Cttz O POI i o 10k 1 201 1 t 404 H 1 104 7 it Ho y 0 9 1 1 6 phosphate Murano acid N Acety IM ramicaold B b Glucose cid 15482 9 3 MHz OH H coo H amino sugars CHZOH CHZOHO 4 p HYLE 10 4 1 H MHz H H B D Galactosamine B D Mariposa mine peony sugars 4 10 1 50 101 1 Fats H0 H HY H OH H OH OH B L Fucose a L Rhamnose H y 0 1 1 4 0 H H H0 FF H0 CHZOH H OH H OH th H b Glllcclronate D Gluconate D Glucono g lactone Acidic sugars 4 3 0 4 H 1 91 14 01 1 OH H N acetylneuraminicacid astatic acid 1 4 0 1 H g OH KOH GCHZOH 4 Ii 31 1 01 1 H OH 4HOTH A D Glllcopyranose CHZOH t H 1 10 1 11 1 H OH HC Hzc c Pyran HO HZ O CHZOH a D Frcictofclranose 1 cn HC CH OH H Fi Fi Furan B D Glclcopyranose B p Frllctofclranose
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