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j. Cosmet. Sci,, 51,253-262 (July/August) Synthesis of N-ethanol-2-(myristyl/palmityl)- a-oxo(stearamide/arachidamide) and its physical properties for a cosmetic raw material BYEONG-DEOG PARK,* MYUNGJIN LEE, YOON KIM,* and JONG KYUNG YOUM, *NeoPharm Co., Ltd., PO Box 306-020, 63-1 Dae-Hwa Dong, Dae Duk-Gu, Daejeon, Korea, AKI Central Research Laboratories, Aekyung Industrial Co. LTD., PO Box 300-200, 72-6 YoungJeon Don& Dong-Gu, Daejeon, Korea. Accepted for publication June 9, 2000. Synopsis As a cosmetic raw material, N-ethanol-2-(myristyl/palmityl)-3-oxo(stearamide/arachidamide) (PC-9 s) has been synthesized and its physical properties have been investigated. PC-9 s was synthesized by the reaction between alkylketene dimer (AKD) and 2-aminoethanol under the ethanol reflux system. The existence of intermolecular hydrogen bonding among the amide groups of PC-9Ss was confirmed by an FT-IR study. PC-9 s showed a very wide range of lamellar liquid crystal formation, with a mixture of fatty acid and cholesterol, and the lamellar structure was formed with a high content of fatty acid composition. The cross-polarized microscopic result of PC-9 s confirmed its intrinsic characteristic of lamellar structure for- mation. PC-9 s was verified to be non-toxic, non-irritable, and non-sensitizing in skin irritation tests on animals and humans. This intrinsic power to form the lamellar structure made it possible to form a multilamellar emulsion, which could have applications in the cosmetic and drug industries. An effective and economical synthetic pathway with high purity and yield facilitates the industrial production of PC-9 s. INTRODUCTION Many physicochemical and biological actions of skin care products in the last decade were concerned with the horny layer of the stratum corneum (SC) (1). The structure of SC was proposed in an illustration as a "brick & mortar" model by Elias in 1981 (2,3). According to the Elias model, the brick represented corneocytes and the mortar repre- sented intercellular lipids. The corneocytes are filled with keratin and embedded in the intercellular lipids that form lamellar structures, which are the origin of the skin barrier function. For this reason, many people have been investigating the components of the intercellular lipids. The main components of intercellular lipids are ceramide, fatty acids, and cholesterol. Ceramide is not only the most prominent lipid found in SC but also an important component for the formation and retention of lameliar structure in SC (4). Topical applications of ceramide or pseudoceramide-containing compositions have been 253