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2311138 Monounsaturated and Polyunsaturated Fatty Acids

May 29, 2018

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    Monounsaturated fatty acids

    contain one double bond

    usually liquid at room temperature

    found primarily in plant foods like avocados,

    olives and nuts and in various vegetable oils

    like olive oil and canola oil

    Common monounsaturated fatty acids are:

    palmitoleic acid

    oleic acid

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    Polyunsaturated fatty acids

    contain two or more double bonds

    like monounsaturated fat, is usually liquid

    at room temperature

    polyunsaturated fat is mostly found in plantfoods like most nuts and in vegetable oils

    like corn, soybean and safflower

    Common polyunsaturated fatty acids are:

    linoleic acidlinolenic acid

    arachidonic acid

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    TO DESCRIBE THE UNSATURATED FATTY ACIDS,

    TWO WAYS ARE OFFERED:

    The chemist's terminology:

    The carbon atoms are counted from the carboxyl

    group which put the emphasis on the double bond

    closest to this group (D-notations)

    As an example: 18:2 (9,12 or cis-9, cis-12-

    octadecadienoic acid, the trivial name: linoleic

    acid

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    The biochemist's and physiologist's terminology:

    Holman RT proposed in 1964 a new numberingsystem for the unsaturation of fatty acids, the "omeganomenclature".

    The double bonds are counted from the methyl groupdetermining the metabolic family, noted by wx (w forthe terminal carbon) or better n-x (n for the total

    number of carbon, x being the position of the distaldouble bond)

    Thus, linoleic acid or cis-9, cis-12-octadecadienoic acidis also named in the shorthand nomenclature 18:2 (n-6). This compound has 18 carbon atoms, 2 double

    bonds and 6 carbon atoms from the last double bondto the terminal methyl group. In the old literature itwas designated 18:2w6.18-6=12, 12-3=9, hence (9,12.

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    NOMENCLATURE

    Fatty acids can be named in many ways:

    symbolic name: given as x:y (( a,b,c) where x is

    the number of Cs in the chain, y is thenumber of double bonds, and a, b, and c are

    the positions of the start of the double bonds

    from C1 - the carboxyl C

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    Example:y OLEIC ACID 18:1( or [

    Oleic acid contains 18 carbon atoms and a double

    bond between positions9

    and 10, indicated by18:1(

    The number 18 indicates the number of carbon

    atoms, 1 indicates the number of double bonds

    and the ( and superscript indicate the position of

    double bond

    Fatty acids may also be classified by the distance

    of the first double bond from the [-carbon

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    systematic name using IUPA

    Cnomenclature. The systematic name

    gives the number of Cs (e.g.

    hexadecanoic acids for 16:0)

    If the fatty acid is unsaturated, the

    base name reflects the number of

    double bonds (e.g. octadecenoic acid for

    18:1 (9 and octadecatrienoic acid for18:3( 9,12,15)

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    Monounsaturated fatty acids contain 1C=C while polyunsaturated fatty acids

    contain more than 1 C=C. Double bonds

    are usual cis.

    There is an alternative to the symbolic

    representation of fatty acids, in which the

    C's are numbered from the distal end (the

    n or w end) of the acyl chain (the otherend from the carboxyl group)

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    Hence 18:3( 9,12,15 could be written as 18:3

    (w -3) or 18:3 (n -3) where the terminal C

    is numbered one and the first double bond

    starts at C3

    Arachidonic acid is an (w -6) fatty acid

    while docosahexaenoic acid is an (w -3)

    fatty acid

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    Symbol common

    name

    systematic

    name

    structure Mp

    (C)

    16:1( Palmitoleicacid

    Hexadecenoicacid

    CH3(CH2)5CH=CH-(CH2)7COOH

    -0.5

    18:1( Oleic acid 9-Octadecenoic

    acid

    CH3(CH2)7CH=CH-

    (CH2)7COOH

    13.4

    18:2( Linoleic

    acid

    9,12 Octadeca-

    dienoic acid

    CH3(CH2)4(CH=CHCH2)2(

    CH2)6COOH

    -9

    18:3( ELinolenic

    acid

    9,12,15 -

    Octadecatrienoic

    acid

    CH3CH2(CH=CHCH2)3(CH

    2)6COOH

    -17

    20:4(5,8,11,14 arachidonic

    acid

    5,8,11,14-

    Eicosatetraenoic

    acid

    CH3(CH2)4(CH=CHCH2)4(

    CH2)2COOH

    -49

    20:5(5,8,11,14,17 EPA 5,8,11,14,17-

    Eicosapentaenoic

    - acid

    CH3CH2(CH=CHCH2)5(CH

    2)2COOH

    -54

    22:6(4,7,10,13,16,19

    DHA Docosohexaenoic

    acid

    22:6w3