1. Field of the Invention
This invention relates to the use of acylated sugar monoacid amides in cosmetic preparations, more especially skin-care and hair-care formulations.
2. Discussion of Related Art
A balanced water content in the individual layers of skin plays an important part in regard to the elasticity and appearance of the skin. The content of bound water is at its greatest in the dermis and in the boundary layer of the epidermis near the basal membrane. The elasticity of the skin is critically determined by the collagen fibrils in the dermis, the specific conformation of the collagen being achieved through the incorporation of water molecules. Destruction of the lipid barrier in the stratum corneum (SC), for example by surfactants, leads to an increase in the transepidermal water loss so that the water-containing surroundings of the cells are destroyed. Since the water bound in deeper layers of skin can only be supplied through vessels via the body fluid and not from outside, it is clear that maintenance of the barrier function of the stratum corneum is essential to the overall condition of the skin [cf. S. E. Friberg et al., C. R. 23rd. CED Congress, Barcelona, 1992, page 29].
Ceramides are lipophilic amides of long-chain fatty acids which are generally derived from sphingosine or phytosphingosine. This class of body fats has acquired considerable significance since they were discovered in the intercellular space between the corneocytes as key components for the buildup of the lipid bilayer, i.e. the permeability barrier, in the stratum corneum of human skin. Ceramides have molecular weights of well below 1,000 so that, when externally applied in a cosmetic formulation, they are able to reach the required point of action. The external application of ceramides results in restoration of the lipid barrier so that the above-mentioned disturbances to the skin function can be causally counteracted [cf. R. D. Petersen, Cosm. Toil. 107, 45 (1992)].
Hitherto, limits have been imposed on the use of ceramides on account of their inadequate availability. Accordingly, attempts have already been made to synthesize ceramide analogs, so-called synthetic barrier lipids (SBL) or pseudoceramides, and to use them for skin care [cf. G. Imokawa et al., J. Soc. Cosmet. Chem. 40, 273 (1989)].
For example, EP-A 0 277 641 and EP-A 0 227 994 (Kao) describe ceramide analogs with the following structure: ##STR2##
EP-A 0 482 860 and EP-A 0 495 624 (Unilever) describe ceramide-related structures corresponding to the following formula: ##STR3##
In addition, sugar derivatives with the following composition: ##STR4## in which R.sup.a is hydrogen or an unsaturated fatty acyl group, z is a number of 7 to 49, R.sup.b is a hydroxyalkyl group and Z is a sugar or phosphate group, are proposed in EP-A 0 455 429 (Unilever) for the protection of skin and hair.
Japanese patent application J7 4043-935 describes acylated N-alkyl-D-gluconamides with the following structure: ##STR5## which are added to resins to improve their flowability, their demoldability or mold release and their electrostripping.
In spite of these various efforts, the results obtained with these substances have so far been unsatisfactory. In particular, the performance level of natural ceramides has never been matched. In addition, the synthesis sequences are technically complicated and therefore expensive which makes the significance of the substances even more relative.
The problem addressed by the present invention was to provide new high-performance ceramide analogs which would be distinguished by a simple synthesis. Another problem addressed by the invention was to provide new compounds based on non-animal raw materials with a structure which would be very close to the ceramides or pseudoceramides.