The preparation of (a.-phthalimidoacyl)malonates via mixed
anhydrides (Ila, b) and subsequent monodeethoxycarbonylation into
the (a.-phthalimidoacyl)acetates (IVa, b) is described. Cyclization ·of
(Illa) with hydroxylamine led to 3-(phthalimidomethyl)isoxazolin-
5-one-4-carboxylic acid (VI), while the malonate derivative (IIIb),
when reacted with hydrazine, gave 4-ethoxycarbonyl-3-(a.-phthalimidoethyl) pyrazolin-5-one (VII). The ketalization of ethyl (phthalimidoacetyl) acetate (!Va) with methyl orthoformate gave methyl
(phthalimidoacetyl)acetate dimethyl ketal (V). The structure of the
obtained compounds is discussed on the basis of their 1H nuclear
magnetic resonance spectra, in some cases supported by infrared
data

A. Nuri

M. Štromar

N. Bregant

English

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CROATICA CHEMICA ACTA CCACAA 47 (4) 595-601 (1975) CCA-903 YU ISSN 0011-1643 547.456 Originai Scientific Paper Preparation and Cyclization of Some B-Keto-Y-Phthalimidoaliphatic Esters N. Bregant, A. Nuri, and M. Stromar Laboratory of Organic Chemistry and B iochemistry, Facuity of Science, and Institute of Organic Chemistry and Biochemistry, University of Zagreb, 41000 Zagreb, Croatia, Yugosiavia Received March 17, 1975 The preparation of (a.-phthalimidoacyl)malonates via mixed anhydrides (Ila, b) and subsequent monodeethoxycarbonylation into the (a.-phthalimidoacyl)acetates (IVa, b) is described. Cyclization ·of (Illa) with hydroxylamine led to 3-(phthalimidomethyl)isoxazolin--5-one-4-carboxylic acid (VI), while the malonate derivative (IIIb), when reacted with hydrazine, gave 4-ethoxycarbonyl-3-(a.-phthali-midoethyl)pyrazolin-5-one (VII). The ketalization of ethyl (phtha-limidoacetyl)acetate (!Va) with methyl orthoformate gave methyl (phthalimidoacetyl)acetate dimethyl ketal (V). The structure of the obtained compounds is discussed on the basis of their 1H nuclear magnetic resonance spectra, in some cases supported by infrared data. Isolation of biologically active substances from Amanita muscaria has stimulated the interest i:n the chemistry of 3-hydroxysoxazoles.1 MuscimoL 3-hydroxy-5-aminomethylisoxazole, isolated from A. muscaria has shown re-markable and multiple biological activity particularly on human central nervous system provoking psychogenic effect2• Brehm et al.3 have confirmed the isoxazole enolbe.tainic structure of muscimol by X-ray crystallogrnphic-methods. Gagneux et al. 4 described the synthesis of 3-hydroxy-5-chlorome-. thylisoxazole from methyl y-chloroacetyl acetate via the corresponding di-methyl ketal and hydroxylamine. Jacquier et al.5 described the preparation of the derivatives of 3-hydroxyisoxazoles from ethylene ketal of appropriate B-ketoesters and hydroxylamine. They stated6 that the relative amounts of the concerned 3-hydroxyisoxazoles and the isomeric isoxazolin-5-ones strongly depend on the constitutions of the B-ketoesters. Recently Krogsgaard-Larsen et al.1 reinvestigated the reaction between. B-ketoesters, protected at a keto group with benzylamine, and hydroxylamine. In contrary to the earlier results8, they have found that the same reactions'. afforded isoxazolin-5-ones, exclusively. The same authors showed that the-method is of general value for the preparation of isoxazolin-5-ones. It was of interest to investigate further the cyclization of B-keto-y-phtha-. limidoesters, as a source of some highly substituted 3-hydroxyisoxazoles. K. Adank et al.9 described the synthesis of d,1-phthalimidoacyl-B-dicar-bonyl compounds. They acylated ethoxy magnesium B-dicarbonyl derivatives'. with acid chlorides of N-phthaloylamino acids. The use of this method was~ 596 N. BREGANT ET AL. applied in 196l1° for the preparation of diethyl (phthalimidoacetyl)malonate in 630/o and ethyl (phthalimidoacetyl-acetate in 62'0/o yield. In our case, however, the reinvestigation of this procedure resulted with 30°/o yield for both com-pounds. In the present paper we described the acylation of diethyl ethoxy magne-sium malonate with mixed anhydrides (Ila, b), prepared from N-phthaloylgly-cine and N-phthaloylalanine, respectively, and ethyl chloroformate. In this way the synthesis of (a-phthalimidoacyl)malonates (Illa, b) and subsequent monodeethoxycarbonylation into (a-phthalimidoacyl)acetates (IVa, b) is per-formed in 35-400/o yields. Scheme I C6H4(C0)2NCH(R)C02H + ClC02Et+ Et3N-+ Et3N · HCl (Ia, b) C6H4(C0)2NCH (R)CO- O-COEt + EtOMgCH(C02Et)2 -+ (Ila, b) steam C5H4(C0)2NCH(R)COCH(C02Et)2 C5H4(C0)2NCH(R)COCH2C02Et dist. 2 h. · (Illa, b) (!Va, b) a; R=H b; R = CHs The ketalization of ethyl (phthalimidoacetyl)ace.tate (IVa) with ethylene glycol is described.11 We performed the ketalization of ·this compound to di-methyl ketal by Claisen's12 method, using methyl orthoformate in absolute methanol. Beside the ketalization the transesterification occured so that the mixture of 510/o of methyl (phthalimidoacetyl)acetate dimethyl ketal and 14.70/o of methyl (phthalimidoacetyl)acetate was isolated. The ketal structure was supported by appearance -of one singlet in the 1H NMR spectrum at S 3.32 ppm befonging to protons of the two methoxy groups, two singlets at 2.77 and 4.12 ppm for two isolated methylenic groups and the singlet at 3.70 ppm for methyl protons of the ester group. Jacquier et al.5 also described the synthesis of 3-hydroxiisoxazoles using B-ketoesters substituted in cc-position and hydroxylamine under basic conditions followed by acidification. We used diethyl (phthalimidoacetyl)malonate (Illa) which is a B-ketoester substituted in the a-position with an ethoxy carbonyl group, to perform the cyclization with hydroxylamine under basic conditions which was followed by immediate acidification. As shown by TLC a mixture of two compounds was formed, one of which gave a violet colour after spraying with FeCl3 reagent. By recrystallization from ethanol-water corresponding substance was isolated. It was found that during the cyclization under descr ibed conditions, the hydrolysis of ethoxycarbonyl group occured and 3-(phthalimidomethyl)iso-xazolin-5-one-4-carboxylic acid (VI) was formed. Its structure was supported by appearance of two signals for unexchangeable protons of the methylene group at 4.17 ppm and of the a110matic ring at 7.83 ppm. The three signals of exchangeable protons were assigned as follows: the sligthly broadened singlet at 10.8 ppm to the proton of the carboxyl group, the singlet at 8.9 ppm, slightly (!Va) (!Ila) (IIIb) ~-KETO-y-PHTHALIMIDOALIPHATIC ESTERS CH(OCHs)s w CHsCOOH Scheme II OCHs I C5H4(C0)2NCHr-C-CH2C02CHa (V) H I I OCHs HOf-C- C-CHzN(C0lzC6H4 I II O=C N '-o/ (VI) (VIa) (VII) 597 broadened too, to the HN< proton of isoxazolin-5-one ring, and the singlet at 3.42 ppm to the methine proton of its C4 tautomer (Vla). The presence of following groups was confirmed by characteristic infrared absorbtions : at 3310 cm-1 v NH-3210 cm-1 associated v OH; 1770, 1718 v C=O of phthalimid; 1710 v C = O (ring); 1680 v C=O (acid); 1610 and 1550 cm-1 v C=N and v C = C respectively. We also performed cyclizaUon of diethyl (u-phthalirmidopropionyl)malonate (IIIb) with hydrazine hydrate in acetic acid under the stream of nitrogen. From the resulted mixture we have isolated 4-ethoxycarbonyl-3-(a-phthalimi-doethyl)pyrazolin-5~one (VII). This derivate of pyrazolin-5-one was examined by TLC, and gave a purple colour after spraying with FeCl3 reagent. The 1H NMR data confirm the structure :13 beside the signal .of the four aromatic protons at 7.87 ppm and the characteristic feature of the ethyl group - triplet at 1.33 ppm and quartet at 4.33 ppm, - the spectrum shows a doublet of methyl protons at 1.80 coupled with the quartet at 6.17 ppm originated by methine proton. The broad singlet at 8.8 ppm of two exchangeable protons 598 N. BREGANT ET AL. is assigned to hydrazo groUJp of the ring. The presence of following groups was confirmed by characteristic infrared absorbtions: at 3380 v NH of hydrazo group, at 1781, 1710 v C=O of phthalimid, while the lower and stronger band is overla'pping with C=O streching modes ·of ester and ring carbonyl, resulting in a broad multiple band 1680 - 1740 cm-1. The ring carbonyl frequency is in this case as well as in the oase of compound (VI) consistent with' the data pu-blished for substituted isoxazolin-5 .... ones.14 The uv spectra of the isoxazolin-5--one derivative (VI), as well as .of the pyrazolin-5-one derivative (VII) are identical with that of N-phthaloy lglycine. EXPERIMEN T AL All melting points are determined on the melting point apparatus by Tottoli and are uncorrected. 'H-NMR spectra were taken on Varian T 60 spectrometer using TMS as a internal standard, ir spectra were revorded on a Perkin Elmer M-137 ,spectrophotometer, uv spectra were obtained on Varian-Techtron UV-VIS model 635 automatic spectrophotometer. For TLC control experiments silicagel HF2s4 (Merck) was used. Preparation of (J-keto-y-phthalimidoaliphatic esters. - General procedure. The mixed anhydride (Ila, b) were prepared by the action of triethylamine and ethyl chloroformate on the N-phthaloylaminoacids in toluene at +2 to +5 °c. The acylations of malonic esters were carried out on the ethoxy magnesium malonate. The ethoxy magnesium malonate in dry ether w as added, at -2 to +2 °c, to the mixed anhydrides. The mixture was allowed to come to room temperature overnight, and was then worked up. Using this procedure the compounds (Illa, b) and (!Va, b) have been prepared, using different work-up procedures as described below. Diethyl (phthalimidoacetyL)maionate (Illa). - To a so1ution of 10.25 g (0.05 mol) of N-phthaloylglycine, 5.05 g (0.05 mol) of triethylamine and 5.4 g (0.05 mol) of ethyl chloroformate in 50 ml toluene the ethereal solution of ethoxy magnesium malonate (0.05 mol) was added. After removal of the volatile material by steam distillation for 15 minutes, the crystalline solid was separated, recrystallized from ethanol; 6.15 g (350/o yield) of compound (Illa) was obtained, white prisms, m. p. 68-69 6C. 1H-NMR spectrum (CDCla) o values : 4.60 ppm (s, lH, -CO- CH-C02-) ; 4.80 ppm and 4.95 ppm (2 s, 2H, ) N-CH2-CO- and enolic); 7.80 ppm (4H, aro-matic); 14.47 ppm (s, lH, OH of the enolic form). The ass ignment of chemical shift value for methylenic protons of the enol form at 4.95 ppm was confirmed by taking the spectrum in pyridin, which showed in addition to lH- singlet for -OH at 14.47 ppm only one singlet for 2H of the methylene group at 4.88 ppm with no evidence for the methine proton. Diethyl (a-phthalimidopropionyl)maLonate (IIIb). - To a solution of 10.95 g (0.05 mol) of N-phthaloylalanine, 5.05 g (0.05 mol) of tritheylamine and 5.4 g (0.05 mol) of ethyl chloroformate in 50 ml toluene the ethereal solution ethoxy magne-sium malonate (0.05 mol) was added. After removal of the volatile material by steam distillation during 15 minutes the separated residual oily product was crystallized from ethanol; 7.6 g (400/o yield) of compound (IIIb) was obtained colourless plates, m . p . 73-74 oc. H 1-NMR spectrum, (CDC13) o values: 1.20 and 1.27 ;ppm (t, two overlapping, 6H, -CH2-CHa) ; 1.70 ppm (d, 3H, CH-CHa); 4.23 ppm (q, 4H, -CH2-CHa); 4.67 ppm (s, -CO-CH-CO-); 5.17 ppm (q, lH -CH-CH3); 7.87 ppm (4H, aromatic H); 13.8 ppm (s, OH of the enolic form). Ethyl (phthaHmidoacetyl)acetate (IVa). - 6.15 g (0.017 mol) of diethyl (phthalimi-doacetyl)malonate (Illa) in 100 ml benzene was subjected to steam distillation for 2 h. The separated crystalline solid 4.13 g (300/o yield) was recrystallized from ethanol; white needles m. p . 111 oc. ~-KETO-y-PHTHALIMIDOALIPHATIC ESTERS 599 1H -NMR spectrum (CDC13), o values: 1.34 ppm (t, 3H, -CH2-CH3); 4.73 ppm (s, 2H, N-CH2-CO-); 4.30 ppm (q, 2H, -CH~CH3); 3.66 ppm (s, 2H, -CO-CH2--CO-O-R); 7.80 ppm (4H, aromatic H). Ethyl (a-phthalimidopropionyl)acetate (IVb). - 3.6 g (0.01 mol) of diethyl (a-phthalimidopropionyl)malonate (IIIb) in 50 ml benzene was subjected to steam distillation for 2 h. The separated oily product was extracted with three 20 ml portions of ether. The combined ether extracts were dried and evaporated in vacuo. Distillation of the residue, b . p . 80-85 °C/0,01 Torr, gave 1.1 g (390/o) of compound (!Vb) as colourless oil:, which slowly crystallized, m. p. 43-44 °c. 1H-NMR spectrum, (CDC13), o values: 1.20 ppm (t, 3T, -CH2-CH3); 1.63 ppm (d, 3H, CH3-CH-CO-); 3.53 ppm (s, 2H, -CO-CH~C02-); 4.17 ppm (q, 2H, 0-CH2-CH3); 5.03 ppm (q, . lH, CH3-CH-CO-) ; 7.7-8.1 ppm (4H, aromatic H) . Anal. C15H15N05 (289.278) calc'd.: C 62.28; H 5.23; N 4.840/o found : C 62.37; H 5.52; N 5.000/o Methyl (phthalimidoacetyl)acetate dimethyl ketal (V). - To a suspension of 8.25 g (0.03 mol) of ethyl (phthalimidoacetyl)acetate and of 13.35 g (13.1 ml; 0.12 mol) of methyl orthoformate in 33 ml absolute methanole, one drop of cone. H2S04 was added and the mixture was left at room temperature for two days with occasional heating to 60-65 °c. Additional seven drops of cone. H2S04 were successively added in course of the reaction. After removing the methyl (phthalimidoac;etyl)acetate, which crystallized from the mixture (800 mg), the filtrate was diluted with 300 ml ether, washed with water to which a few drops of 250/o ammonia h ad previously been added and dried (MgS04). After evaporation of ether under reduced pressure the crystalline solid gave 8.5 g of a mixture of two compounds. Fractional crystallization from ethyl acetate-petroleum other yielded 4.7 g (510/o) white hexahedrons m.p. 92-100 °c of methyl (phthalimidoacetyl)acetate dimethyl ketal and additional 350 mg (overall yield 1.15 g; 14.7-0/o) m. p. 137-139 °c., long w hite prisms of methyl (phthalimidoacetyl)acetate were isolated. The analytical sample of (V) was recry-stallized from ethyl acetate petroleum ether, m. p. 118-119 °c. 1H-NMR spectrum, (CDC13), o values: 2.77 ppm (s, 2H, -CH2-C02CHa); 3.32 ppm (s, 6H, -C(OCH3)2); 3.70 ppm (s, 3H, .-C02CHs); 4.12 ppm (s, 2H, ) N-CH2--C-); 7.8 ppm (4H, aromatic H) . Ir (KBr): 2845, 2825 (two methoxy groups); 1779, 1718 (phthalimid), 1748 cm-1 (ester). Anal. C15H11N06 (307.077) calc'd.: C 58.67; H 5.57; N 4.560/o found: C 58.90; H 5.51; N 4.370/o The analytical sample of methyl (phthalimidoacetyl)acetate recrystallized from ethyl acetate petroleum ether, m. p . 138-139 °c. 1H-n. m . r. spectrum, (CDC13), o values: 3.60 ppm (s, 2H, -CO-CH~); 3.77 ppm (s, 3H, -C02CH3); 4.67 ppm- (s, 2H>N-CH2-C-); 7.8 ppm (4H, aromatic H). Ir (KBr); 1785, 1755, 1723 and 1415 cm-1• Anal. C1sH11N05 (261.23) calc'd.: C 59.76; H 4.24; N 5.360/o found: C 59.53; H 4.18; N 5.22; 3-(Phthalimidomethyl)isoxazolin-5-one-4-carboxylic acid (IV). - To a stirred solution of 1.39 g (0.02 mol) of hydroxylammonium chloride and 1.6 g (0.04 mol) -0f sodium hydroxide in 20 ml water ,a suspension of 6.95 g (0.02 mol) of diethyl (phthalimidoacetyl)malonate (IIIa) in 30 ml ethanol was edded in small portions during 30 min. at 0-5 °c. The mixture was stirred until being homogeneous and diluted with 6 ml of water. After standing at 4 9C for 1 h. the mixture was acidified to pH=2 using cone. HCl. TLC (benzene:ethyl acetate:formic acid 30:30:2) showed two spots, one of which gave a violet colour after spraying with FeC13• The cry-stalline precipitate was filtered off, and dried to give 1.86 g of 3-(phthalimidome-thyl)isoxazolin-5-one-4-carboxylic acid (VI); pale pink needles m . p. 185- 6 °c. The filtrate was extracted with three 50 ml portions of ether: petroleum ether (4:1). The combined extracts were dried (MgS04) and evaporated to oily residue which crystallized after standing. After crystallization from ethanol:water, 0.74 g m. p. 600 N. BREGANT ET AL. 185-6 °c of (VI) was obtained; the overall yield of pure 3-(phthalimidomethyl)iso-xazolin-5-one-4-carboxylic acid (VI) was 2.6 g (45°/lf), m. p. 185-6 °c. 1H-NMR spectrum, (DMSO) o values: 3.42 ppm and 8.9 ppm (2s, lH methine proton at C4 of isoxazolin-5-one ring and HN ( of the tautomeric isoxazolin-5-one ring Vla); 4.17 ppm (s, 2H, ) N-CH~C=C); 7.83 ppm (s, 4H, aromatic H); 10.8 ppm (s, lH -COOH). Ir (KBr) : 3310, 3210, 1770, 1718, 1710, 1680 and 1610 cm-1• Anal. C13H80 6N2 (288.162) calc'd.: C 54.18; H 2.77; N 9.720/o found: C 54.39; H 2.46; N 9.520/o 4-Ethoxycarbonyl-3-(a-phthalimidoethyl)pyrazolin-5-one (VII). - To a mixture of 3.6 g (O.ol mol) of diethyl (a-phthalimidopropinoyl)malonate (Illb) and 16 ml of acetic acid, 0.48 ml (0.50 g; 0.01 mol) of hydrazine hydrate was added. The resulting mixture was heated at 95-100 ()C for 3 hours, under a stream of nitrogen. The reaction mixture was evaporated under reduced pressure to dryness, the residue disolved in 30 ml of CH2Ch, washed with three 15 ml portions of water and dried (MgS04) . After evaporating of dichloromethane, 2.5 g (75.90/o) of a pale yellow oil was obtained. The TLC control (benzene :ethyl:acetate:formic acid 30 :30:2) showed the crude product to be complex mixture, which after crystallization from acetone: ether:cyclohexane (2:2:1), gave colourless prisms, 1.04 g (31.60/o), m . p. 178-181 °'C. (TLC of the sample showed only one spot giving a purple colour after spraying with FeC13 reagent) . 1H-NMR spectrum (CDC13) o values: 1.33 ppm (t, 3H, -CH2CH8); 1.80 ppm (d, 3H, CH3-CH); 4.33 ppm (q, 2H, -CH~CHa); 6.17 ppm (q, lH, HC-CHa); 7.87 ppm (4H, aromatic H); 8.8 ppm (broad signal, lH + lH, -HN-NH-). Ir (KBr): 3380, 2600, 3000, 1780, 1710, 1615, 1570, 1510, 1385, 1330 and 1100 cm-1• Anal. C16H1sNsOs (329.0) calc'd .: C 58.36; H 4.56; N 12.770/o found: C 58,07; H 4.43; N 12.590/o. Acknowledgements. The authors are indebted to dr. V. Sunjic for valuable comments on the manuscript, and to ing. P. Kuretic for valuable technical assistance. To the Republic Research Fund of Croatia we are grateful for the financial support. REFERENCES 1. C. H . Eu gs t er, Fortschr. Chem. Org. Naturst. 27 (1969) 261. 2. G. A. R. J oh n st on, D. R. Curtis, W. C. D e Gr o at, and A. W. Dug-g an, Biochem. Pharmacol. 17 (1968) 2488; P. G. Waser, D. H. In Efron, B. Ho 1 ms t e d t, and N. S. K 1 in e, Ethnopharmacologic Search for Psycho-active Drugs, Public Health Service Publication No. 1645, U. S. Government Printing Office, Washington D. C. 1967, p. 419; W. Theo b a 1 d, 0 . B ii ch, H. A. Kunz, P . Krupp, E. G. Stenger, and H. Heimann, Arzneim. Forsch. 18 (1968) 311; S. Ga mu 1 in, Bull. Sci., Cons. Acad RSF Yugoslavie, 12 (1967) 122; ibid., 15 (1970) 241; ibid., p ; 246 p. 247. 3. L. B re h m, H. H j e d s, P. Krog s g a a rd - L a rs en, Acta Chem. Scand. 26 (1972) 1298. 4. A. R. Gagneux, F. Hafliger, C. H . Eugster, and R. Good, Tetra-hedron Lett. (1965) 2077. 5. R. Jacquier, C. Petrus, F. Petrus, and J. Verducci, Bull. Soc. Chim. Fr. (1970) 1978; idem., ibid., p. 2685. 6. R. Jacquier, F. Petrus, J. Verducci, and Y. Vida 1, Bull. Soc. Chim. Fr. (1971) 3664. 7. P. Krogsgaard-Larsen, S. Br0gger Christensen, andH. Hjeds, Acta Chem. Scand. 27 (1973) 2802. 8. K. B ow den, G. Crank, and W. J. Ro s s, J . Chem. Soc. (1968) 172. 9. K. Ad an k, H. A. Pfenning er, W. G. St o 11, and M. Visconti n i, Helv. Chim. Acta 44 (1961) 2131. 10. J. K. Mehrotra, S. D. Verma, J . Indian. Chem. Soc. 38 (1961) 785. 11. B. Loev, J. W. Wilson, and M. M. Goodman, J. Med. Chem. 13 (1970) 738. J3-KETO-y-PHTHALIMIDOALIPHATIC ESTERS 601 12. L. C 1 a is en, Ber. 47 (1914) 3171. 13. A. R. Kat r it z k y, F. W. Maine, Tetrahedron 20 (1964) 299. 14. R. J a cu i er, C. Petrus, F. Petrus, and J . Verducci, BuLl. Soc Chim. Fr. (1970) 2690. SAZETAK Priredivanje i ciklizacija nekih ~-keto-y-ftalimido alkil estera N. Bregant, A. Nuri i M. Stromar Opisana je priprema (u-ftalimidoacil)malonata (IIIa, b) pomocu mjesovitih anhidrida (Ila, b), te njihovo monodeetoksikarboniliranje u (u-ftalimidoacil)acetate (!Va, b). Ciklizacija dietil(ftalimidoacetil)malonata (!Ila) s hidroksilaminom dala je 3-(ftalimidometil)izoksazolin-5-on-4-karboksilna kiselinu (VI), dok je malonski deri-vat (IIIb) reakcijom s hidrazinom dao 4-etoksikarbonil-3-(u-ftalimidoetil)pirazolin--5-on (VII). Spoj (!Va) djelovanjem metilortoformijata u apsolutnom metanolu dao je metil(ftalimidoacetil)acetat-dimetil-ketal (V). Strukture opisanih spojeva razma-trane su na osnovi podataka dobivenih iz spektara 1H-nuklearne magnetske rezonan-cije, kao i infracrvenih spektara. ZA VOD ZA ORGANSKU KEMIJU I BIOKEMIJU PRIRODOSLOVNO-MATEMATICKOG FAKULTETA i INSTITUT ZA ORGANSKU KEMIJU I BIOKEMIJU SVEUCILISTA U ZAGREBU 41000 ZAGREB Prispjelo 17. ozujka 1975 

Preparation and Cyclization of Some B-Keto-Y-Phthalimidoaliphatic Esters

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