N-substituted P-menthane carboxamides

Description

COOLING COMPOUNDS ARE PRESENTED

Cooling compounds, that is, chemical compounds that impart a cooling sensation to the skin or the mucous membranes of the body, are well known to the art and are widely used in a variety of products such as foodstuffs, tobacco products, beverages, dentifrices, mouthwashes and toiletries.

One class of cooling compounds that have enjoyed substantial success consists of N-substituted p-menthane carboxamides. Examples of these compounds are described in, for example, British Patents GB 1,351,761-2 and U.S. Pat. No. 4,150,052.

It has now been found that a particular selection of such compounds exhibits a cooling effect that is both surprisingly strong and long-lasting. In one embodiment, the cooling compounds can be represented by formula I

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in which m is 0 or 1, Y and Z are selected independently from the group consisting of H, OH, C1-C4 straight or branched alkyl, and a C1-C4 straight or branched alkoxy; X is (CH₂)_n—R, where n is 0 or 1 and R is a group with non-bonding electrons, with the provisos that:

(a) when Y and Z are H, X is not F, OH, MeO or NO₂in the 4-position and is not OH in the 2 or 6-position
(b) when Y or Z is H then X, Y and Z are such that
- (i) the groups in the 3- and 4-positions are not both OMe,
- (ii) the groups in the 4- and 5-positions are not both OMe,
- (iii) the groups in 3- and 5-positions are not OMe if the group in the 4-position is OH, and
- (iv) the groups in the 3- and 5-positions are not OH if the group in the 4-position is methyl.

An embodiment provides for compounds of formula I wherein X is in the 4-position. Additional embodiments provide for compounds of formula I wherein X is in the 4-position and Y and Z are H, OH, Me or OMe. In certain embodiments, Y and Z are selected independently.

Useful groups with non-bonding electrons are halogens, OH, OMe, NO₂, CN, Ac, SO₂NH₂, CHO, CO₂H and C₁-C₄alkyl carboxylates such as CO₂Et. Other C₁-C₄alkyl carboxylates with non-bonding electrons may be useful.

The compounds of formula I have 3 chiral centres, giving rise to 8 stereoisomers. All possible stereoisomers are included in the scope of the compounds represented by formula I.

The cooling compounds may be prepared by reacting an arylalkylamine derivative with an appropriate acid chloride or carbonyl chloride. The carbonyl chloride can be prepared from 1-menthol ((1R,2S,5R)-2-isopropyl-5-methylcyclohexanol).

The cooling compounds are distinguished from similar compounds of the prior art by their surprisingly high cooling effect (up to 10 times higher than that of similar known compounds) and by the longevity of the cooling effect, which adds to their attractiveness in a large variety of products.

For example, a small group of panelists was asked to taste various solutions of cooling compounds and indicate which solutions had a cooling intensity similar or slightly higher than that of a solution of menthol at 2 ppm. In a second experiment, the same panel was asked to taste the solutions at the chosen concentrations and to record the cooling intensity at regular time intervals until no cooling could be sensed in the mouth. Results are shown in table 1.

TABLE 1

experiment on cooling intensity and longevity.

Chemical
Concentration
Longevity

1-Menthol
2.0 ppm
35 minutes

N-ethyl p-menthanecarboxamide (WS-3)
1.5 ppm
57 minutes

Formula 1, m = 0,Y = Z = H,
0.5 ppm
90 minutes

X = 4-CN

Formula 1, m = 0, Y = Z = H,
0.2 ppm
93 minutes

X = 4-CH₂CN

From Table 1, it can be seen that the compounds of Formula I are up to 10 times stronger and last up to 3 times longer than menthol, the reference cooling compound. Compounds of Formula I are also much stronger and last longer than WS-3, a known cooling compound of the prior art.

The subject cooling compounds may be used in products that are applied to the mouth or the skin to give a cooling sensation. By “applying” is meant any form of bringing into contact, for example, oral ingestion or, in the case of tobacco products, inhalation. In the case of application to the skin, it may be, for example, by including the compound in a cream or salve, or in a sprayable composition. A method is directed to providing a cooling effect to the mouth or skin by applying thereto a product comprising a compound as hereinabove described.

The subject cooling compounds may be used alone or in combination with other cooling compounds known in the art, e.g., menthol, menthone, isopulegol, N-ethyl p-menthanecarboxamide (WS-3), N,2,3-trimethyl-2-isopropylbutanamide (WS-23), menthyl lactate (Frescolat™ ML), menthone glycerine acetal (Frescolat™ MGA), mono-menthyl succinate (Physcool™), mono-menthyl glutarate, O-menthyl glycerine (CoolAct™ 10), menthyl-N,N-dimethylsuccinamate or 2-sec-butylcyclohexanone (Freskomenthe™).

The subject cooling compounds and related methods are further described by the following non-limiting examples.

The starting compound p-menthane-3-carbonyl chloride as used for the preparation of the compounds in Example 1-6 was prepared from 1-menthol.

EXAMPLE 1
Preparation of N-(4-cyanomethylphenyl) p-menthanecarboxamide

To a flask, were added 6.6 g (50 mmol) of 4-aminobenzyl cyanide, 4.04 mL of pyridine and 100 mL MtBE. To this mixture, 10 g of p-menthane-3-carbon*yl chloride were added dropwise over 5 minutes. The reaction mixture was stirred for 24 h. To the reaction mixture, 50 mL of water were added. The mixture was separated. The organic layer was washed with 50 mL of water and 50 mL of brine. The organic layer was dried over MgSO₄. The solvent was evaporated in vacuo to afford the crude product, which was recrystallized from hexanes to afford 10.1 g of the desired product with the following spectroscopic properties:

MS: 299 ([M+1]), 298 ([M⁺]), 132, 83. ¹H NMR (300 MHz; CDCl₃) δ; 7.58 (d, 2H), 7.49 (s, 1H), 7.27 (d, 2H), 3.73 (s, 2H), 2.2 (t, 1H), 1.96-1.57 (m, 5H), 1.48-1.21 (m, 2H), 1.172-0.99 (m, 2H), 0.94 (d, 3H), 0.93 (d, 3H), 0.85 (d, 3H). ¹³C NMR (75 MHz; CDCl₃)δ: 174.4, 137.8, 128.3, 125.1, 120.3, 118.2, 50.5, 44.3, 39.25, 34.3, 32.1, 28.7, 23.8, 22.9, 22.1, 21.2, 16.1

EXAMPLE 2
Preparation of N-(4-sulfamoylphenyl) p-menthanecarboxamide