Synthesis and characterization of long-chain tartaric acid diamides as novel ceramide-like compounds

Article abstract of DOI:10.3390/molecules15020824

Ceramides play a crucial role in the barrier function of the skin as well as in transmembrane signaling. In this study long aliphatic chain tartaric acid diamides able to replace ceramides in an in vitro model of the stratum corneum lipid matrix due to their similar physico-chemical properties were synthesized from diacetoxysuccinic anhydride in four steps. Their pro-apoptotic effect on fibroblast cells was also investigated.

Full text of DOI:10.3390/molecules15020824

Molecules 2010, 15, 824-833; doi:10.3390/molecules15020824
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Characterization of Long-Chain Tartaric Acid
Diamides as Novel Ceramide-Like Compounds
Bálint Sinkó 1, Melinda Pálfi 2, Szabolcs Béni 1, József Kökösi 1 and Krisztina Takács-Novák 1,*
1
Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes E.u.9., Budapest H-
1092, Hungary; E-Mails: sinbal@gytk.sote.hu (B.S.); beniszabi@gytk.sote.hu (S.B.);
kozsef@gytk.sote.hu (J.K.)
2
Department of Pharmacodynamics, Semmelweis University, Nagyvárad tér 4., Budapest H-1089,
Hungary; E-Mail: melinda.palfi@net.sote.hu (M.P.)
∗ Author to whom correspondence should be addressed; E-Mail: novkri@gytk.sote.hu;
Tel.: +36-1-215-5241; Fax: +36-1-217-0891.
Received: 22 January 2010; in revised form: 1 February 2010 / Accepted: 3 February 2010 /
Published: 5 February 2010
Abstract: Ceramides play a crucial role in the barrier function of the skin as well as in
transmembrane signaling. In this study long aliphatic chain tartaric acid diamides able to
replace ceramides in an in vitro model of the stratum corneum lipid matrix due to their
similar physico-chemical properties were synthesized from diacetoxysuccinic anhydride in
four steps. Their pro-apoptotic effect on fibroblast cells was also investigated.
Keywords: ceramide-analogues; tartradiamides; transdermal penetration; apoptosis
1. Introduction
The skin acts as a major target as well as a principle barrier for transdermal drug delivery [1]. The
stratum corneum plays a crucial role in the barrier function for topical drug penetration. Numerous
methods have been developed to predict the penetration through the stratum corneum, but all these
methods suffer several limitations [2,3]. There is a major need for a quick and effective model in early
stages of drug discovery, because the possibility of applying drugs transdermally offers fundamental
advantages compared to other routes of administration. The Parallel Artificial Membrane Permeability

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Assay (PAMPA) [4] can be a good method for this purpose provided it applies artificial membrane
similar to stratum corneum.
As main barrier of the skin, the stratum corneum lipid matrix contains as the predominant
components about 50% of ceramides, 35% of free fatty acids and 15% of cholesterol; its behavior is
different from other biological membranes. Ceramide (N-fatty acyl sphingosine) is the lipid moiety of
sphingomyelin and all types of glycosphingolipids. In human stratum corneum eight subclasses of
ceramides have been identified, which differ from each other by the head group architecture and the
alkyl chain lengths [5]. The alkyl chain lengths distribution is bimodal, the most abundant chain length
is C24-C26, but there is a small fraction of ceramides having an acyl chain length of C16-C18 mainly
responsible for penetration properties. Recently, the function of ceramide as second messenger in
transmembrane signaling has been the subject of great interest [6,7]. They play an important role in
regulating the transmission mechanisms of the signals controlled by the membrane sphingolipids [8].
The endogenous ceramides used in cosmetics are expensive natural extracts, they are mixtures in
which the N-acyl chain is saturated or unsaturated and may contain a hydroxyl substituent in the alpha
position relative to the carbonyl group. In order to replace the endogenous ceramides in artificial
membrane of skin PAMPA model, our aim was to develop synthetic ceramide analogues that are able
to mimic their effects, are stable enough against metabolization and cheap enough for HT method.
Tartaric acid serves as a good basis for the synthesis of ceramides-analogues as its 2,3-diol subunit is
able to form hydrogen bonds similarly to real ceramides (Figure 1).
Figure 1. The structure of ceramide 2 and tartramide (C16-C16).
Natural L-(+)-tartaric acid is one of the cheapest enantiomerically pure organic compounds
available. It is a polar, polyfunctional and chiral molecule with the absolute configuration of (2R,3R),
and with a C2 axis of symmetry. Tartaric acid derivatives have been the subject of numerous studies
and display selective ion complexation or ion transport [9], chiral recognition [10] and molecular
catalysis [11]. Since tartaric acid esters are hydrolytically too labile [12], the aim was to synthesize
long chain tartaric acid amides (tartramides). A 10 member series of ceramide analogues was designed,
where the polar portion of ceramide has been replaced by an inverse bioisosteric amide and the
lipophilic portion of the C18 alkyl moiety of ceramide has been replaced with various long chain

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(8–18) alkylamines. Stereochemically, both ceramides and tartramides contain two chiral carbon
centers and form four stereoisomers: two enantiomeric pairs of erythro and threo-diastereomers.
2. Results and Discussion
2.1. Synthesis of tartaric acid diamides
In the literature several synthetic routes are known for preparation of tartramides, including
pyrolysis of alkylammonium tartarate [10], microwave condensation of tartaric acid with different
amines [13,14], and amidation of tartaric acid esters or OH-protected tartaric dichloride [11]. For the
synthesis of nonsymmetrical tartramides a multistep reaction route was developed [15]. After
formation of tartaric acid monoamide it was reacted with a dehydrating agent to obtain
N-alkyltartrimide by ring closure, then a ring opening reaction with another aliphatic amide lead to the
nonsymmetrical tartramide. The cited synthetic routes have been developed for the preparation of short
alkyl chain derivatives, as the long chain amines (>12) failed to react with tartrimide, even after longer
heating at reflux temperature. The aim of this work was to develop a route which is suitable for the
synthesis of long alkyl chain tartradiamides.
Scheme 1. Synthesis of tartaric acid diamides 5.
Formation of cyclic tartrimide 4 from tartaric acid 6 via tartaric anhydride 8 using trifluoroacetic
anhydride lead to formation of O-acetylated side product and ring opened diamide. Prolonged thermal
heating of the monoammonium salt 7 in toluene under azeotropic reflux also provided various amounts
of amide product 9, depending on the chain length (Scheme 1/b). The products are difficult to purify,
which causes diamide mixture formation in the last step. These methods are only useful in small scale.
The scale up of these reactions greatly increases the quantity of undesired side products. After
reinvestigation of literature methods we have found that a convenient access to the desired products
necessitates multistep approach using O-protected tartaric anhydride.

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Compounds 5a-j were prepared as shown in Scheme 1/a. Treatment of (R,R)-diacetoxysuccinic
anhydride (1) with the appropriate long-chain amines in THF at room temperature overnight lead to
diacetoxysuccinamides 2a-d in high yield. Small amounts of ammonium salt of products could be
isolated by filtration, which were crystallized from the reaction mixture. Ring closure of
compounds 2a-d with excess thionyl chloride in the presence of catalytic amount of pyridine at 70 °C
for 15 min provided the alkyltartrimide derivatives 3a-d as thick semisolid compounds, which were
used directly in the next step. Deacetylation of compounds 3a-d with acetyl chloride/ethanol mixture
afforded the appropriate tartrimide derivatives 4a-d in good yield. The products were crystallized from
the reaction mixtures and isolated by filtration. The reaction of compounds 4a-d with excess of amines
in xylene at 130 °C for 24 h yields the tartramides 5a-j. Amine catalyzed racemisation was observed
during these reactions, depending on the chain length. The isomer ratio of the products was determined
by NMR spectroscopy. Eight of the ten tartramides (5b, 5c, 5d, 5f, 5g, 5h, 5i, 5j) are new
chemical entities.
2.2. Characterization of tartaric acid diamides
The 1H- and 13C-NMR spectra of chiral tartaric acid derivatives were completely assigned based on
one and homo- and heteronuclear two dimensional NMR experiments (COSY, HSQC, HMBC). The
1H-NMR spectra of compounds 5f-j were recorded in dilute solution, as a pronounced decrease in
solubility was observed in case of long chain derivatives. The isomeric ratio has also been determined
by NMR in dilute solution at 35 °C, in order to exclude the misinterpretation originating from the
1
different solubility of the isomers. According to earlier H spectroscopic studies of tartaric acid
diamides, two set of signals were observed in case of the final products [15]. The small rate of
isomerisation on the chiral centers of the (2R,3R)-tartaric moiety occurred only in the last step of the
synthesis, resulted the two set of signals. The characteristic NMR peaks of (R,R) isomers were
observed at 3.25 ppm (-CH2-NH-), 4.23 ppm (HO-CH-) and 5.50 ppm (-OH) respectively, while the
(RS/SR) product exhibited signals at 3.29 ppm (-CH2-NH-), 4.00 ppm (HO-CH-) and 5.70 ppm (-OH).
For the detailed 1H- and 13C-NMR assignments and MS data see the Experimental section.
2.3. Proapoptotic effect of tartaric acid diamides
As ceramides are key mediators in apoptosis [16], preliminary apoptotic studies were performed
with compounds 5a-j as follows: primer mouse embryonic fibroblasts were incubated with 10-5 mol/L
of the compounds for 24 h and nucleosomal DNA fragmentation, a marker of apoptotic cell death, was
analyzed by flow cytometry. Apoptotic cells are identified by their subdiploid DNA content after
staining with the DNA intercalating dye, propidium iodide [17–19]. The percents of apoptotic cells
corresponding to the sub-G1 phase were found to be not significantly different from those prepared
with pure solvent that proved the absence of ceramide-like pro-apoptotic activity, which is an
advantage for transdermal delivery systems (Figure 2). Compounds 5a-j were also tested in the
PAMPA (Parallel Artificial Membrane Permeability Assay) stratum corneum lipid matrix model [20].

Molecules 2010, 15
Figure 2. The pro-apoptotic effect of the newly synthesized compounds compared to pure
828
solvent (compounds are considered pro-apoptotic over the rate of 20%).
3. Experimental Section
3.1. General
All the chemicals were from Sigma-Aldrich. Melting points of compounds were determined on a
Stuart Scientific Digital Melting Point Apparatus SMP3. Mass spectra were obtained on a Agilent
1
Technologies 6410 Triplequad LC/MS instrument. H-NMR and 13C-NMR were recorded on a 600
MHz Varian VNMRJ spectrometer equipped with a dual 5-mm inverse-detection gradient (IDPFG)
probehead using TMS as internal reference. Proapoptotic effect was measured on FACSCalibur (Becton
Dickinson, San Jose, CA, USA) flow cytometer using the CellQuest 3.1 (Becton Dickinson) software.
3.2. General procedure for the synthesis of compounds 2a-d
(R,R)-4-(Acetyloxy)-2,5-dioxooxolan-3-yl acetate (1, 25 mmol) was reacted with appropriate amine
(25 mmol) in THF (40 mL) at room temperature overnight. Small amounts of the ammonium salts of
products could be isolated by filtration, were crystallized from the reaction mixture. Then THF was
removed under reduced pressure giving the 2,3-bis(acetyloxy)-3-(alkylcarbamoyl)propanoic acids 2a-d.
1
2,3-bis(Acetyloxy)-3-(octylcarbamoyl)propanoic acid (2a). Yield: 86%; pale yellow oil; H-NMR
(CDCl3) δ: 6.35 (1H; t; NH; J = 6 Hz), 5.75 (1H; d; CH; J = 2.4 Hz), 5.57 (1H; d; CH; J = 2.4 Hz),
3.32 (1H; m; NH-CH2), 3.19 (1H; m; NH-CH2), 2.17 (3H; s; CH3-COO), 2.11 (3H; s; CH3-COO), 1.49
(2H; tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.31-1.19 (10H; m; CH2), 0.86 (3H; t; CH3; J = 7.2 Hz);
isomer ratio (RR/RS:SR): 100:0.
1
2,3-bis(Acetyloxy)-3-(dodecylcarbamoyl)propanoic acid (2b). Yield: 80%; yellowish oil; H-NMR
(CDCl3) δ: 6.25 (1H; t; NH; J = 6 Hz), 5.78 (1H; d; CH; J = 2.4 Hz), 5.61 (1H; d; CH; J = 2.4 Hz),
3.36 (1H; m; N-CH2), 3.23 (1H; m; N-CH2), 2.20 (3H; s; CH3-COO), 2.13 (3H; s; CH3-COO), 1.49
(2H; tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.34–1.20 (18H; m; CH2), 0.88 (3H; t; CH3; J = 6.9 Hz);
isomer ratio (RR/RS:SR): 100:0.
2,3-bis(Acetyloxy)-3-(hexadecylcarbamoyl)propanoic acid (2c). Yield: 81%; m.p. 76–78 °C; 1H-NMR
(MeOD) δ: 5.62 (1H; d; CH; J = 2.4 Hz), 5.60 (1H; d; CH; J = 2,4 Hz), 3.25 (1H; m; NH-CH2), 3.19

Molecules 2010, 15
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(1H; m; NH-CH2), 2.18 (3H; s; CH3-COO), 2.13 (3H; s; CH3-COO), 1.51 (2H; tt; NH-CH2-CH2; J =
7.2, 6.6 Hz), 1.35-1.22 (26H; m; CH2), 0.92 (3H; t; CH3; J = 7.2 Hz); isomer ratio (RR/RS:SR): 100:0.
1
2,3-bis(Acetyloxy)-3-(octadecylcarbamoyl)propanoic acid (2d). Yield: 60%; m.p. 127–129 °C; H-
NMR (CDCl3) δ: 6.25 (1H; t; NH; J = 6 Hz), 5.78 (1H; d; CH; J = 2.4 Hz), 5.62 (1H; d; CH; J = 2,4
Hz), 3.36 (1H; m; NH-CH2), 3.23 (1H; m; NH-CH2), 2.20 (3H; s; CH3-COO), 2.14 (3H; s; CH3-COO),
1.52 (2H; tt; NH-CH2-CH2; J = 6.6, 6.0 Hz), 1.38–1.20 (30H; m; CH2), 0.88 (3H; t; CH3; J = 7.2 Hz);
isomer ratio (RR/RS:SR): 100:0.
3.3. General procedure for the synthesis of compounds 3a-d
2,3-bis(Acetyloxy)-3-(alkylcarbamoyl)propanoic acid 2a-d (19 mmol) was treated with thionyl
chloride (45 mL) and pyridine (0.7 mL) at 70 °C for 15 min. After evaporating the thionyl chloride, the
4-(acetyloxy)-1-alkyl-2,5-dioxopyrrolidin-3-yl acetate 3a-d was purified on activated carbon in
dichloromethane (15 mL). After evaporation of dichloromethane the product appears as a semisolid,
which was used directly in the next step.
1
4-(Acetyloxy)-1-octyl-2,5-dioxopyrrolidin-3-yl acetate (3a). Yield: 78%; semisolid wax; H-NMR
(DMSO-d6) δ: 5.77 (2H; s; CH), 3.42 (1H; m; N-CH2), 3.39 (1H; m; N-CH2), 2.13 (6H; s; CH3-COO),
1.47 (2H; tt; NH-CH2-CH2; J = 6.6, 6.0 Hz), 1.27-1.16 (10H; m; CH2), 0.84 (3H; t; CH3; J = 6.9 Hz);
isomer ratio (RR/RS:SR): 100:0.
1
4-(Acetyloxy)-1-dodecyl-2,5-dioxopyrrolidin-3-yl acetate (3b). Yield: 85%; semisolid wax; H-NMR
(DMSO-d6) δ: 5.77 (2H; s; CH), 3.43 (1H; m; N-CH2), 3.39 (1H; m; N-CH2), 2.14 (6H; s; CH3-COO),
1.49 (2H; tt; NH-CH2-CH2; J = 6.6, 6.0 Hz), 1.28–1.18 (18H; m; CH2), 0.85 (3H; t; CH3; J = 6.9 Hz);
isomer ratio (RR/RS:SR): 100:0.
4-(Acetyloxy)-1-hexadecyl-2,5-dioxopyrrolidin-3-yl acetate (3c). Yield: 82%; brownish semisolid wax;
1H-NMR (DMSO-d6) δ: 5.76 (2H; s; CH), 3.43 (1H; m; N-CH2), 3.39 (1H; m; N-CH2), 2.14 (6H; s;
CH3-COO), 1.49 (2H; tt; NH-CH2-CH2; J = 6.6, 6.0 Hz), 1.29–1.18 (26H; m; CH2), 0.85 (3H; t; CH3;
J = 6.9 Hz); isomer ratio (RR/RS:SR): 100:0.
4-(Acetyloxy)-1-octadecyl-2,5-dioxopyrrolidin-3-yl acetate (3d). Yield: 79%; brownish semisolid wax;
1H-NMR (DMSO-d6) δ: 5.76 (2H; s; CH), 3.42 (1H; m; N-CH2), 3.38 (1H; m; N-CH2), 2.15 (6H; s;
CH3-COO), 1.50 (2H; tt; NH-CH2-CH2; J = 6.6, 6.0 Hz), 1.31–1.20 (30H; m; CH2), 0.84 (3H; t; CH3;
J = 7.2 Hz); isomer ratio (RR/RS:SR): 100:0.
3.4. General procedure for the synthesis of compounds 4a-d
The 4-(acetyloxy)-1-alkyl-2,5-dioxopyrrolidin-3-yl acetates 3a-d (15 mmol) were deacetylated by
dissolving them in ethanol (90 mL) and slowly adding acetyl chloride (20 mL) at 0 °C, then stirring the
mixture for 1 day at room temperature. The precipitated white crystalline 3,4-dihydroxy-1-alkyl-
pyrrolidine-2,5-dione products 4a-d were filtered and washed with ethanol.

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1
3,4-Dihydroxy-1-octylpyrrolidine-2,5-dione (4a). Yield: 76%; m.p. 127–129 °C; H-NMR (CDCl3) δ:
4.57 (2H; s; CH), 3.54 (1H; m; NH-CH2), 3.50 (1H; m; NH-CH2), 1.56 (2H; m; NH-CH2-CH2), 1.32–
1.22 (10H; m; CH2), 0.88 (3H; t; CH3; J = 7.2 Hz); isomer ratio (RR/RS:SR): 100:0.
1
1-Dodecyl-3,4-dihydroxypyrrolidine-2,5-dione (4b). Yield: 83%; m.p. 142–144 °C; H-NMR (CDCl3)
δ: 4.58 (2H; s; CH), 3.55 (1H; m; NH-CH2), 3.50 (1H; m; NH-CH2), 1.58 (2H; m; NH-CH2-CH2),
1.36–1.21 (18H; m; CH2), 0.88 (3H; t; CH3; J = 7.2 Hz); isomer ratio (RR/RS:SR): 100:0.
1
1-Hexadecyl-3,4-dihydroxypyrrolidine-2,5-dione (4c). Yield: 81%; m.p. 140–142 °C; H-NMR
(DMSO-d6) δ: 4.32 (2H; s; CH), 3.54 (1H; m; NH-CH2), 3.50 (1H; m; NH-CH2), 1.56 (2H; m; NH-
CH2-CH2), 1.32-1.22 (26H; m; CH2), 0.88 (3H; t; CH3; J = 7.2 Hz); isomer ratio (RR/RS:SR): 100:0.
1
3,4-Dihydroxy-1-octadecylpyrrolidine-2,5-dione (4d). Yield: 75%; m.p. 132–134 °C; H-NMR
(CDCl3) δ: 4.57 (2H; s; CH), 3.54 (1H; m; NH-CH2), 3.50 (1H; m; NH-CH2), 1.56 (2H; m; NH-CH2-
CH2), 1.32-1.21 (30H; m; CH2), 0.88 (3H; t; CH3; J = 7.2 Hz); isomer ratio (RR/RS:SR): 100:0.
3.5. General procedure for the synthesis of compounds 5a-j
3,4-Dihydroxy-1-alkylpyrrolidine-2,5-dione 4a-d (4 mmol) was treated with appropriate amine (8
mmol) in xylene (50 mL) at 130 °C for 24 h. The white crystalline 2,3-dihydroxy-N,N'-dialkyl-
butanediamide product 5a-j was filtered and washed with hot ethanol.
1
2,3-Dihydroxy-N,N'-dioctylbutanediamide (5a). Yield: 79%; m.p. 172–174 °C; H-NMR (CDCl3) δ:
7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.28H; s; OH), 5.50 (1.72H; d; OH; J = 6.6 Hz), 4.23 (1.72H; d; CH;
J = 6.6 Hz), 4.00 (0.28H; s; CH), 3.29 (0.56H; m; NH-CH2), 3.24 (3.44H; m; NH-CH2), 1.50 (4H; tt;
13
NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.37–1.22 (20H; m; CH2), 0.88 (6H; t; CH3; J = 7.0 Hz); C-NMR
(CDCl3) δ: 174.6, 70.8, 39.8, 32.5, 30.0, 29.9, 29.8, 27.4, 23.3, 14.7; isomer ratio (RR/RS:SR): 86:14;
MS (ESI) m/z: 373 (MH+).
1
N-Dodecyl-2,3-dihydroxy-N'-octylbutanediamide (5b). Yield: 75%; m.p. 166–168 °C; H-NMR
(CDCl3) δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.22H; s; OH), 5.50 (1.78H; d; OH; J = 6.6 Hz), 4.23
(1.78H; d; CH; J = 6.6 Hz), 4.00 (0.22H; s; CH), 3.29 (0.44H; m; NH-CH2), 3.24 (3.56H; m; NH-
CH2), 1.50 (4H; tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.37-1.22 (28H; m; CH2), 0.88 (6H; t; CH3; J = 6.9
13
Hz); C-NMR (CDCl3) δ: 174.6, 70.6, 39.8, 32.6, 30.34, 30.31, 30.28, 30.21, 30.04, 29.9, 29.8, 27.4,
23.4, 14.8; isomer ratio (RR/RS:SR): 89:11; MS (ESI) m/z: 429 (MH+).
1
N-Hexadecyl-2,3-dihydroxy-N'-octylbutanediamide (5c). Yield: 93%; m.p. 161–163 °C; H-NMR
(CDCl3) δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.40H; s; OH), 5.50 (1.60H; d; OH; J = 6.6 Hz), 4.23
(1.60H; d; CH; J = 6.6 Hz), 4.00 (0.40H; s; CH), 3.29 (0.80H; m; NH-CH2), 3.24 (3.20H; m;
NH-CH2), 1.50 (4H; tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38-1.22 (36H; m; CH2), 0.88 (6H; t; CH3;
13
J = 6.7 Hz); C-NMR (CDCl3) δ: 174.6, 70.6, 39.8, 32.6, 30.38, 30.34, 30.31, 30.28, 30.21, 30.11,
30.04, 30.00, 29.96, 29.93, 29.86, 27.4, 23.4, 14.8; isomer ratio (RR/RS:SR): 80:20; MS (ESI) m/z: 485
(MH+).

Molecules 2010, 15
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1
2,3-Dihydroxy-N-octadecyl-N'-octylbutanediamide (5d). Yield: 92%; m.p. 163–165 °C; H-NMR
(CDCl3) δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.36H; s; OH), 5.50 (1.64H; d; OH; J = 6.6 Hz), 4.23
(1.64H; d; CH; J = 6.6 Hz), 4.00 (0.36H; s; CH), 3.29 (0.72H; m; NH-CH2), 3.24 (3.28H; m;
NH-CH2), 1.50 (4H; tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38-1.22 (40H; m; CH2), 0.88 (6H; t; CH3;
13
J = 6.7 Hz); C-NMR (CDCl3) δ: 174.6, 70.6, 39.8, 32.6, 30.39, 30.35, 30.33, 30.29, 30.26, 30.22,
30.16, 30.11, 30.07, 30.04, 29.99, 29.93, 29.86, 27.4, 23.4, 14.8; isomer ratio (RR/RS:SR): 82:18; MS
(ESI) m/z: 513 (MH+).
N,N'-Didodecyl-2,3-dihydroxybutanediamide (5e). Yield: 86%; m.p. 155–157 °C; 1H-NMR (CDCl3) δ:
7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.28H; s; OH), 5.50 (1.72H; d; OH; J = 6.6 Hz), 4.23 (1.72H; d; CH;
J = 6.6 Hz), 4.00 (0.28H; s; CH), 3.29 (0.56H; m; NH-CH2), 3.24 (3.44H; m; NH-CH2), 1.50 (4H; tt;
13
NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38-1.22 (36H; m; CH2), 0.88 (6H; t; CH3; J = 6.9 Hz); C-NMR
(CDCl3) δ: 173.6, 70.8, 39.8, 32.6, 30.32, 30.28, 30.24, 30.21, 30.14, 30.04, 29.92, 27.5, 23.4, 14.8;
isomer ratio (RR/RS:SR): 86:14; MS (ESI) m/z: 485 (MH+).
1
N-Dodecyl-N'-hexadecyl-2,3-dihydroxybutanediamide (5f). Yield: 86%; m.p. 157–159 °C; H-NMR
(CDCl3) δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.38H; br s; OH), 5.50 (1.62H; br s; OH), 4.23 (1.62H; br
s; CH), 4.00 (0.38H; br s; CH), 3.29 (0.76H; m; NH-CH2), 3.24 (3.24H; m; NH-CH2), 1.50 (4H; tt;
13
NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38-1.22 (44H; m; CH2), 0.88 (6H; t; CH3; J = 6.7 Hz); C-NMR
(CDCl3) δ: 173.5, 70.6, 39.8, 32.6, 30.39, 30.35, 30.32, 30.29, 30.25, 30.23, 30.21, 30.19, 30.04, 30.00,
29.91, 27.5, 23.4, 14.8; isomer ratio (RR/RS:SR): 81:19; MS (ESI) m/z: 541 (MH+).
1
N-Dodecyl-2,3-dihydroxy-N'-octadecylbutanediamide (5g). Yield: 56%; m.p. 151–154 °C; H-NMR
(CDCl3) δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.46H; s; OH), 5.50 (1.54H; d; OH; J = 6.6 Hz), 4.23
(1.54H; d; CH; J = 6.6 Hz), 4.00 (0.46H; s; CH), 3.29 (0.92H; m; NH-CH2), 3.24 (3.08H; m;
NH-CH2), 1.50 (4H; tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38–1.22 (48H; m; CH2), 0.88 (6H; t; CH3;
13
J = 6.7 Hz); C-NMR (CDCl3) δ: 173.6, 70.6, 39.8, 32.6, 30.39, 30.35, 30.32, 30.29, 30.27, 30.24,
30.22, 30.20, 30.17, 30.14, 30.10, 30.04, 29.93, 27.5, 23.4, 14.8; isomer ratio (RR/RS:SR): 77:23; MS
(ESI) m/z: 569 (MH+).
N,N'-Dihexadecyl-2,3-dihydroxybutanediamide (5h). Yield: 96%; m.p. 157–159 °C; 1H-NMR (CDCl3)
δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.34H; s; OH), 5.50 (1.66H; d; OH; J = 6.6 Hz), 4.23 (1.66H; d;
CH; J = 6.6 Hz), 4.00 (0.34H; s; CH), 3.29 (0.68H; m; NH-CH2), 3.24 (3.32H; m; NH-CH2), 1.50 (4H;
tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38–1.22 (52H; m; CH2), 0.88 (6H; t; CH3; J = 6.8 Hz); 13C-NMR
(CDCl3) δ: 173.6, 70.8, 39.8, 32.6, 30.39, 30.37, 30.35, 30.32, 30.29, 30.26, 30.22, 30.19, 30.05, 30.01,
29.92, 27.5, 23.3, 14.8; isomer ratio (RR/RS:SR): 86:14; MS (ESI) m/z: 597 (MH+).
1
N-Hexadecyl-2,3-dihydroxy-N'-octadecylbutanediamide (5i). Yield: 82%; m.p. 151–153 °C; H-NMR
(CDCl3) δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.40H; s; OH), 5.50 (1.60H; d; OH; J = 6.6 Hz), 4.23
(1.60H; d; CH; J = 6.6 Hz), 4.00 (0.40H; s; CH), 3.29 (0.80H; m; NH-CH2), 3.24 (3.20H; m;
NH-CH2), 1.50 (4H; tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38-1.22 (56H; m; CH2), 0.88 (6H; t; CH3;
13
J = 6.8 Hz); C-NMR (CDCl3) δ: 173.6, 70.8, 39.8, 32.6, 30.39, 30.37, 30.35, 30.31, 30.26, 30.22,

Molecules 2010, 15
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30.19, 30.15, 30.12, 30.08, 30.05, 30.01, 29.92, 27.5, 23.4, 14.8; isomer ratio (RR/RS:SR): 80:20; MS
(ESI) m/z: 625 (MH+).
1
2,3-Dihydroxy-N,N'-dioctadecylbutanediamide (5j). Yield: 91%; m.p. 151–153 °C; H-NMR (CDCl3)
δ: 7.08 (2H; t; NH; J = 6 Hz), 5.70 (0.60H; s; OH), 5.50 (1.40H; d; OH; J = 6.6 Hz), 4.23 (1.40H; d;
CH; J = 6.6 Hz), 4.00 (0.60H; s; CH), 3.29 (1.20H; m; NH-CH2), 3.24 (2.80H; m; NH-CH2), 1.50 (4H;
tt; NH-CH2-CH2; J = 7.2, 6.6 Hz), 1.38–1.22 (60H; m; CH2), 0.88 (6H; t; CH3; J = 6.9 Hz); 13C-NMR
(CDCl3) δ: 173.4, 70.9, 39.8, 32.6, 30.38, 30.35, 30.31, 30.29, 30.26, 30.23, 30.19, 30.15, 30.10, 30.07,
30.05, 30.00, 29.92, 27.5, 23.3, 14.8; isomer ratio (RR/RS:SR): 70:30; MS (ESI) m/z: 653 (MH+).
4. Conclusions
In this study long aliphatic chain tartramides which are able to replace ceramides in in vitro model
of stratum corneum lipid matrix were synthesized. It can also be concluded that the ceramide-like
tartramides, if applied as host penetration enhancer compounds and based on their proapotopic effects,
exhibit high degrees of safety, and their inclusion enables the gradual release of medicines, agricultural
chemicals and perfumes and the reduction of the emergent toxicity thereof. Therefore, it can be
supposed that the long chain tartaric acid amide derivatives have very meaningful future in the
medicinal chemistry.
Acknowledgements
K. Takács-Novák thanks the Hungarian National Science Foundation (Grant No.: OTKA K 78102)
for financial support. The authors also thank Mária Takács for NMR measurement.
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Sample Availability: Samples of the compounds 5a-j are available from the authors.
© 2010 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
This article is an open-access article distributed under the terms and conditions of the Creative
Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).