*4carbohydrates - cyclic aldoses - glycosides - heterocyclic aromatics

Download *4Carbohydrates - Cyclic Aldoses - Glycosides - Heterocyclic Aromatics

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  • 1) Carbohydrates: Formula (& how they fit into Life)

  • 2) Carbohydrates: Fischer projections Is D-glyceraldehyde a carbohydrate ?

  • 3) Carbohydrates: Naming (Generic)

  • 4) Carbohydrates: Configurations

    The product will be a 1,5-dicarbonyl compound

  • 5) Carbohydrates: Enantiomers + Diasteromers

    Maximum Number of Possible Stereoisomers

    (including meso compounds) 2 n

  • 6) Carbohydrates: Optical Rotation

  • Forming Hemiacetals of Aldoses INTRAmolecular attack of OH on an aldehyde

  • Amino (Deoxy) Sugars contain an -NH2 group in place of an -OH group

    CHO

    OHOHHNH2

    HH

    HOH

    CH2OH

    CHO

    OHOHHH

    HH

    HOH2N

    CH2OH

    CHO

    OHOHHNHCCH3

    HH

    HOH

    CH2OH

    OCHO

    OHHHNH2

    HHOHOH

    CH2OH

    4

    2

    D-Mannosamine(C-2 stereoisomer of D-glucosamine

    D-Glucosamine D-Galactosamine(C-4 stereoisomer of D-glucosamine)

    N-Acetyl-D-glucosamine

    three amino sugars are common in nature: !D-glucosamine, D-mannosamine, and D-galactosamine!

  • 1) Cyclic Aldose Rxns: Acylation

    The OH groups of monosaccharides exhibit the same chemistry as typical alcohols

    Ac can be used as an abbreviation for the acetyl group, CH3-C=O

    All OH groups react.

  • 2) Cyclic Aldose Rxns: Alkylation

    All OH groups react.

    The OH groups of monosaccharides exhibit the same chemistry as typical alcohols

  • The acetal of a monosaccharide is called a glycoside.

    3A) Cyclic Aldose Rxns: Formation of Glycosides

    Heat

    By-Product is water + H2O

    Key Point: Ethanol is used in the example (above), but ANY alcohol (i.e. an OH group on another carbohydrate) can be used.

    This is how well make disaccharides, oligosaccharides, and polysaccharides.

    The name ends with oside.

    The anomeric carbon (the carbon with an OR and OH groups) is more activated than the others.

    Hemiacetal (anomeric carbon with OR and OH) becomes an Acetal (anomeric carbon with OR and OR)

  • 3B) Cyclic Aldose Rxns: Mechanism of Glycoside Formation

  • 4) Cyclic Aldose Rxns: Formation of an N-Glycoside

    More Examples

  • Glycoside (Acetal) Hydrolysis Glycosides (Acetals) can be hydrolyzed with acid(aq) + heat

    + heat

  • Glycoside (Acetal) Hydrolysis: Mechanism Glycosides (Acetals) can be hydrolyzed with acid (aq) + heat

    + heat

  • 1

    Heterocyclic Aromatic Compounds: Heterocycles are any cyclic compound that

    contains at least one heteroatom (N, O, S, P) in a ring Aromaticity is a bit more complex

    Aromaticity = stability = unreactive

  • 2

    Criteria for Aromaticity

    [1] A molecule must be cyclic.

  • 3

    [2] A molecule must be completely conjugated. Aromatic compounds must have a p orbital on every atom.

    Criteria for Aromaticity

    To be aromatic, each p orbital must overlap with

    p orbitals on adjacent atoms.

  • 4

    [3] A molecule must be planar. All adjacent p orbitals must be aligned so that the electron density can be delocalized.

    Since cyclooctatetraene is non-planar, it is not aromatic, and it undergoes addition reactions just like those of other alkenes.

    Criteria for Aromaticity

  • 5

    [4] A molecule must satisfy Hckels rule, and contain a particular number of electrons.

    Hckel's rule:

    Criteria for Aromaticity

    Erich Hckel

  • 6

    [5] A heteroatom with an sp3 lone (non-bonding) pair of electrons will re-hybridize to a p-orbital to obtain aromaticity (to satisfy Hckel number of electrons).

    [6] Carbonyl Groups have very polar bonds. So, you can consider them as:

    Criteria for Aromaticity

  • 7

    N pyridine

    Pyridine: -electron structure (6 -electrons) The nitrogen lone pair electrons are not part of the aromatic system.

  • 8

    + B:H

    H H H H

    HH+ B:H

    cyclopropenyl anion4 -electrons

    1

    2 3

    Cyclopropenyl anion

    6 electrons (a Hckel number)

    aromatic

    4 electrons (NOT a Hckel number)

    anti-aromatic

    HH

    H H

    HH + B:

    H

    H H

    HH + B:H

    cyclopentadienyl anion6 -electrons

    1

    2 3

    4 5

    pKa ~ 16

    Cyclopentadienyl anion

  • Examples: heterocyclic aromatic compounds

    Cytotoxin- Inhibits DNA-topoisomerase enzymes

  • NN

    Me

    N NHMe

    NNC

    H

    H

    Ovarian & lung cancer GSK - Topotecan

    Pfizer - Irinotecan

    Camptothecin Analogues

    Treating stomach & intestinal ulcers

    Examples: heterocyclic aromatic compounds