GB2239019A - Making optical isomers of carbohydrates - Google Patents

Abstract

A method of producing an L-type sugar from the corresponding D-type sugar is disclosed, it involves the steps of treating the D-type sugar to break C-C bonds, whereby at least some of the C-C bonds reform to give an L-type configuration and separating the L-type sugar from the D-type sugar. The L-type sugars may be produced by irradiation of the D-type sugar or by genetic manipulation of plant sources. The sugars produced find use in dietary control or in the treatment of diabetics.

Description

Title: Methods of making carbohydrates and their uses DESCRIPTION This invention concerns methods of making carbohydrates and in particular sugars and their uses.

Carbohydrates are polyhydroxy aldehydes or ketones or those products which are chemically related to such simple units by combination of two or more of these units through the loss of water. These higher units are thus anhydrides. They yield the simple units, referred to above, by treatment with acids such as hydrochloric or sulphuric and particularly with enzymes.

Carbohydrates may be classified as monosaccharides, disaccharides and polysaccharides. Monosaccharides are the simple units and di- and polysaccharides can be hydrolysed to form monosaccharides. Mono- and disaccharides are known as sugars. Well known examples of monosaccharides include glucose (desctrose), galactose, mannose and fructose (laevulose).

Examples of disaccharides include sucrose which hydrolyses to dextrose and laevulose and lactose which hydrolyses to glucose galactose.

Monosaccharides may be designated as right-handed or left-handed according to the configuration about the furthest asymetric carbon atom from the carbonyl group.

The symbols used are D- for right-handed and L- for left handed i.e. when the -OH group on the asymetric carbon atom is on the right or left. It is believed that most if not all naturally occurring sugars are or are made up of right-handed monosaccharides. For example both naturally occurring glucose and fructose are right-handed and sucrose hydrolyses to D-glucose and D-fructose.

Sucrose is normally broken down in the body by insulin to form D-glucose which is in turn carried by the bloodstream to the tissues, where it is oxidised ultimately to carbon dioxide and water with the release of energy. Some of the D-glucose converted into fats; some reacts with nitrogen-containing components to form amino acids, which in turn are combined to form proteins that may make up a large part of the body. As a result, in diabetes, large amounts of unused sugar appear in the blood and overflow into the urine.

Intermediary products in the metabolism of fats and proteins, ketone or acetone bodies, also appear in the blood and urine, and their presence in large amounts is associated with diabetic coma and acidosis.

The symptons of diabetes are weakness, weight loss, excessive appetite and thirst, and the excretion of excessive amounts of urine. Treatment with insulin can alleviate the problems of diabetes. But dietary control alone or in addition to insulin treatment is important. Principally, the amount of sugar taken in the diet has to be controlled so that either any insulin created in the body can cope or administration of insulin can be kept to a minimum.

Carbohydrates in the diet can be obtained from other sources than sucrose so that a reduction in its intake is possible. However, diabetics then have to suffer from lack of sweetness in the taste of their food. Artificial sweetners have been used as substitutes for natural sugar but can have undesirable side effects.

As has been mentioned above, naturally occurring sugars are entirely or at least mainly of the D-type and it is believed that the enzymes in the body are orientated to lock onto the D-type sugars in order to break them down. It is envisaged, therefore, that L-type sugars will not be so broken down by enzymes in the body. Thus diabetics could for example enjoy the sweet taste of L-type sugars without the problems associated with D-glucose i.e. L-type sugars would pass harmlessly through the body.

Proposals for synthesis of various L-type sugars have been made, although no commercial exploitation of products of such syntheses appears to have occurred, presumably because it has not been possible to produce sufficient quantities of L-type sugars at commercially viable prices.

An object of this invention is to provide methods of producing L-type sugars.

According to one aspect of the invention it is proposed that an L-type sugar be formed by molecular reconstruction of the corresponding D-type sugar.

It may be possible to break C-C bonds in the D-type sugar responsible for its D-formation whereby at least a proportion thereof will reform to give an L-formation. The L-formation sugars produced may then be separated from the D-formation sugars by a suitable means such as by biological or chemical means.

One possibility may be to bathe a D-sugar with, for example slow neutrons, laser energy or photons say of about l.e.v., so that C-C bonds are broken and reformed, whereby some of the bonds will be reformed in the L-configurations rather than the D-configuration and then to separate the various end products.

In addition to producing L-type sugars in the laboratory, it is envisaged that L-type sugars be produced from natural sources by suitable modification of the natural source, for example, by genetic manipulation of cane or beet sugar.

It may be possible to irradiate cane or beet sugar seed to produce L-type mutants including L-cane or L-beet seeds and then to separate the L-seeds for use in propogating L-type plants. Then L-type sugars may be extracted from those plants.

Alternatively genetic engineering on cane or beet sugar plant seeds may be used to produce seeds for plants capable of producing the desired L-sugars.

Separation of L- and D-type products may be by any suitable method say using physical properties, such as melting points, or by removing D-type products by reaction with naturally occuring reactants therefor not reactive with L-type products.

Thus, the invention is concerned with the production of sugars such as L-glucose and L-fructose as well as disaccharides that hydrolyse to monosaccharides at least one of which is an L-type monosaccharide.

The invention thus also proposes, for example, methods of producing a sucrose that hydrolyses to L-glucose and L-fructose and a lactose that hydrolys.es to L-glucose and L-galactose.

These are, of course, only examples of a wide variety of L-type sugars that may be produced according to the invention The following Table shows existing and proposed sugars and their relationship.

Table of Heptose Sugars (16 possibilities) Sugar/Chirality - = Left Hand (LH) + = Right Hand (RH) L6N Glucose SinistroseL Dextrose Fructose T Aristocranose q Rectose Q Mannose h Scrumpose W < Cidrose NOTES.

L = from the Latin for left and right.

G = from the Greek for left and right.

W = from West English.

N = accurs in Nature (3 out of possible 16 only) A = found in apples.

X = formerly called Laevulose because solution transmits light with anti clockwise rotation of plane of polarisation: this name to be abandoned because it wrongly suggests it is a LH heptose sugar.

NB (1) Fructose is about twice as sweet as glucose, (2) physical and chemical properties of sugars differ and (3) taste is not affected by chirality.

It is envisaged that sugars produced in the methods of the invention will be used, inter alia, for treatment or aid of diabetics and for use in dietary control for the overweight.

Claims (3)

C=MS

1. A method of producing an I-type sugar from the corresponding D-type sugar comprising the steps of treating the D-type sugar to bream C-C bonds, whereby at least some C-C bonds reform to give an L-type configuration instead of a D-type formation, and separating the L-type sugar from the D-type sugar.

2. A method as claimed in claim 1, wherein the treatment comprises irradiation of the D-type sugar.

3. A method as claimed in claim 1 or 2 carried out on D-sugar containing seeds.