Hydroxyproline

4- hydroxypyrrolidine - 2-carboxylic acid

• 51-35-4 (2S, 4R)
• 618-27-9 (2S, 4S)
• 3398-22-9 (2R, 4S)
• 2584-71-6 (2R, 4R)

Colorless solid

Fixed

• 274 ° C [ (2S, 4R) -4-hydroxyproline ]
• 238-241 ° C. [( 2S, 4S) -4-hydroxyproline ]

Good in water (500 g · l-1 at 20 ° C)

Template: Infobox chemical / molecular formula search available

Hydroxyproline ( L-4- hydroxyproline exact ) is an α - amino acid found in collagen chemically bonded. The exact designation of the naturally occurring amino acid is ( 2S, 4R )-4- hydroxypyrrolidine - 2-carboxylic acid.

L-4- hydroxyproline is produced by hydroxylation in the 4-position on the pyrrolidine ring of L- proline which is incorporated into a polypeptide chain (protein ) of a collagen molecule. The enzyme prolyl hydroxylase catalyzes this with the participation of ascorbic acid ( vitamin C). Hydroxyproline in the collagen molecule stabilizes the integrity of the collagen triple helix via a gauche effect. The theory that emanating from hydroxyproline hydrogen bonds stabilize the triple helix is considered to be refuted. 4- hydroxypyrrolidine -2 -carboxylic acid, exists in four stereoisomers, in our environment plays only the (2S, 4R ) isomer as a proteinogenic amino acid is a part. Enantiomer with the natural (2S, 4R )-form, the ( 2R, 4S )-form. The (2S, 4S)- form and (2R, 4R )-form of the diastereomers are proteinogenic (2S, 4R )-4- hydroxypyrrolidine - 2-carboxylic acid [ Synonym: (2S, 4R) -4-hydroxyproline ].

If in the literature and in this article of hydroxyproline - without any additives - is mentioned, the natural ( 2S, 4R)- hydroxyproline [ Synonym: L-4- hydroxyproline ] meant.

Properties

Hydroxyproline is in pure form predominantly as " inner salt " or zwitterion, whose formation can be explained by the fact that the proton of the carboxyl group migrates to the lone pair of the nitrogen atom of the amino group.

In an electric field, the zwitterion migrates not because it is not loaded as a whole. Strictly speaking, this is at the isoelectric point ( a certain pH value) of the case in which hydroxyproline its lowest solubility in water. The other two stereoisomers of (2S, 4S) - and ( 2R, 4R )-configuration so as form zwitterions.

Physiological function

Hydroxyproline is not directly genetically encoded, but occurs as post-translational modification. In collagen built L- proline is hydroxylated by the enzyme prolyl 4- hydroxylase and with the participation of vitamin C to L- hydroxyproline. Hydroxyproline is required for its mechanical properties as a structural protein. The deficiency disease scurvy results in a connective tissue with reduced or no content of hydroxyproline and hydroxylysine in collagen.

Pathophysiology

When Osteitis deformans, chronic overactivity of osteoclasts is increased hydroxyproline released by bone loss. The hydroxyproline can be determined in urine for the diagnosis.

Production and recovery

The acid hydrolysis of collagen obtained by the neutralization of a protein hydrolyzate of proteinogenic α -amino acids. This one wins today by ion exchange L -hydroxyproline commercially.

Chemistry and Applications

(2S, 4R )-N- acetyl-4 -hydroxyproline (INN: Oxaceprol ) is a drug against degenerative joint disease. For the multi-step synthesis of an ACE inhibitor is (2S, 4R )-4 -hydroxyproline used as starting material. Is thermally decarboxylated by heating in tetraethylene glycol dimethyl ether in the presence of catalytic amounts of cyclohexene -3-one to give the cyclic chiral amino alcohol (R )-3- hydroxypyrrolidine.

Structural isomers of four 4- Hydroxyproline are four stereoisomeric 3- Hydroxyproline of little importance.

Determination of hydroxyproline

The quantitative analysis of hydroxyproline is used to determine the Bindegewebsanteils in meat products. The quality of meat is instructive, since hydroxyproline is found only in collagen and thus instrumental in connective tissue ( tendons, bone, cartilage and skin parts ); therefore, a high content of hydroxyproline considered as an indication of an increased use of inferior raw materials. After measurement of the total Kjeldahl nitrogen of BEFFE value can be calculated.

The sample is digested with hydrochloric acid to and hydrolyzed polypeptides are broken down into amino acids. The fat is separated and the amino acids are oxidized with chloramine-T. The oxidation product forms with p- dimethylaminobenzaldehyde red colored condensation product. This is quantitatively detected photometrically at 558 nm.