Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2003-03-28
2004-04-20
Powers, Fiona T. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06723856
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ‘an improved process for the preparation of 2-acetyl-1-pyrroline, the principle aroma component of basmati and other varieties of scented rice and also of processed cereal and grain products’.
The main uses of the present invention are, i) preparation of 2-acetyl-1-pyrroline by a simple process and ii) making the aroma chemical in grams. The flavor chemical is of great value, in the art of application of flavor to foodstuffs like rice and bakery products.
BACKGROUND AND PRIOR ART REFERENCES
Scented varieties of rice
1-6
will have a characteristic, strong aroma when cooked. ‘Basmati’ varieties in Southeastern Asia, ‘Della’ in America, ‘Milagrosa’ in Philippines, ‘Khao Dawk Mali 105’ in Thailand, ‘Seratus Malam’ in Indonesia and ‘Heiri’ in Japan are examples of such varieties. All over the world, they are highly valued and used in making rice dishes and other food products.
2-acetyl-1-pyrroline was first identified in 1982 by Buttery et al
7-8
, who described its odour as that of cooked rice and popcorn-like. They also described a method of its synthesis from 2-acetylpyrrole
9
. Also, a method for its quantitative analysis was developed by Buttery et al
10
and refined later by Tanchotikul et al
11
. It can be used, among other things, to evaluate the flavor of new rice varieties. Steam distillation cum continuous extraction isolation procedure (Likens-Nickerson method) is used for isolating the rice flavor. 2,4,6-trimethylpyridine (collidine) is added as internal standard to the flask containing rice and water. The volatile basic fraction is separated from other volatiles that are extracted into the organic solvent (diethyl ether) by adding dilute sulfuric acid and stirring. In this way, compounds interfering in the GC analysis are removed. After extraction, the basic compounds are regenerated from the aqueous acid by neutralization with excess sodium bicarbonate and re-extracted with ether. The extract after concentration (~to 0.05 ml), can be analyzed by GC. The amount of 2-Acetyl Pyrroline (AP) is calculated by the following equation.
2
-AP concentration (ppb)
=
area of AP peak
area of TMP peak
×
150
×
3.57
×
5
A recovery factor of 28% is recommended, for inclusion as determined by the stability of pure 2-AP, under the conditions employed for extraction. Hence, it is necessary to multiply the results based on the internal standard and then by the factor 100/28=3.57 to get the amount of 2-acetyl-1-pyrroline actually present in the cooked rice. The factor 150 is the number of micrograms of the internal standard added and the factor 5 is needed to convert to ppb. Another method by Tonchitkul et al
11
., employs the SDE method for extraction and selected ion monitoring (SIM) in GC-MS for detection and quantification of 2-acetyl-1-pyrroline and trimethylpyridine. 2-AP is found to be present in all scented rice varieties in quantities ranging from 300 to 750 ppb.
Mol. formula: C
6
H
9
ON;
Mol. Wt. 111;
CAS Registry No:85213-22-5;
Structural Formula
2-acetyl-1-pyrroline can be characterized by a comparison of its retention time and MS data with those of a reference standard or those reported in literature. The mass spectrum of 2-acetyl-1-pyrroline has major peaks at m/z 111(M
+
, 5% abundance, 83 (11), 69 (11), 68 (8), 55(2), 52 (0.2) and 43 (100), 42 (24) and 41 (50). It's Kovats index is 1320 on a Pyrex glass capillary column coated with Carbowax 20M. Its IR spectrum in CCl
4
displays absorption maxima at 1695, 1620, 1435, 1370, 1340, 1250, 1080, 1000, 975 and 940 cm
−1
.
The compound is a colorless liquid when freshly prepared and purified. It must be protected from light and air and preserved in sealed vials under vacuum at temperatures below −20° C. Even under these conditions, it is reported to turn to red and eventually become very dark on long storage. A conjugated polymer, resulting from the coupling of the carbonyl group of one molecule with the 5-position of another molecule, is believed to be the product formed in the process
9
. For this reason the compound is more stable and better preserved in dilute solutions, especially aqueous ones, for several months at less than 20° C.
It seems reasonable to assume that 2-acetyl-1-pyrroline has a similar origin to the bread aroma compound, 2-acetyl-1,4,5,6-tetrahydropyridine
12
. It is assumed that the intermediate formed after decarboxylation of proline residue, is hydrolyzed with the formation of 1-pyrroline. 2-acetyl-1-pyrroline results from the acetylation 1-pyrroline by 2-oxopropanal. Many syntheses of 2-acetyl-1-pyrroline are reported in recent literature
13-17
.
Reference may be made to the synthetic method (Buttery et al.
J. Agric. Food Chem
. 1983, 31, 823-826) starting from 2-acetyl-1-pyrrole. The main drawback of this procedure is that it employs, for reduction, expensive rhodium on alumina catalyst in stoichiometric quantities, because its activity is lost during the reaction. The subsequent oxidative step is inefficient as it affords low yields (less than 10%) and the product requires sophisticated preparative GC for purification.
Reference may be made to the synthetic method of DeKimpe N G et al. (
J. Agric. Food Chem
. 1993, 41, 1458-1461), wherein pyrrolidine is converted into tripyrroline, which on hydrocyanation yields 2-cyano-1-pyrroline in two steps and subsequently to 2-acetyl-1-pyrroline by Grignard reaction with methylmagnesium bromide or iodide. The main drawback of this procedure is that it has multiple steps and employs potassium cyanide reagent and generation of hydrogen cyanide, both of which are highly toxic.
Reference may be made to another method (Guttmann S, Helv. Chim Acta 1961, 44, 721-744; Hausler and Schmidt, Liebigs Ann. Chem. 1979, 1881-1889; Poisel H and Schmidt U, Chem Ber, 1975, 108, 2547-2553) wherein proline is converted to its methyl ester by passing dry HCl through a methanolic solution of proline or by reaction with thionyl chloride in dry methanol. The drawback of both these methods is that they involve laborious steps of repeated methanol addition and its removal to obtain the hydrochloride of the methyl ester. The methyl ester is then liberated and dried for N-chlorination followed by dehydrohalogenation using triethylamine to afford 2-(methoxycarbonyl)-1-pyrroline. This reaction is very slow (>24 h) and it also gives rise to side products. This precursor is then treated with methylmagnesium iodide to afford 2-acetyl-1-pyrroline.
Reference may be made to another method (Hoffmann T and Schieberle P,
J. Agric. Food Chem
. 1998, 46, 616-619) wherein 2-acetyl-1-pyrroline is prepared from N-(tert-butoxycarbonyl)-1-proline in four steps. The drawback of this invention is that it involves sulfur containing 2-pyridylthio intermediate, traces of which could interfere with the olfactory purity of the flavourant.
Reference may be made to yet another study (Favino T F et al. J. Org. Chem. 1996, 61, 8975-8979) wherein 2-acetyl-1-pyrroline is prepared by Penicilin acylase-mediated hydrolysis of 1-[(N-phenylacetyl)amino]4,5-dioxohexane to 1-amino4,5-diketone compound followed by spontaneous ring closure of the latter. The drawback of this method is that, the preparation of N-phenylacetamide derivative involves multiple steps of conversion starting from cis-3-hexenol via the corresponding acetylenic C-6 amine.
OBJECTS OF THE INVENTION
The main objective of the present invention is to develop ‘an improved process for preparation of 2-acetyl-1-pyrroline, a principal basmati aroma component’, which obviates the aforesaid drawbacks of the processes described in the prior art.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides, an improved process for preparation of 2-acetyl-1-pyrroline, the basmati rice flavourant’, by synthesis of 2-acetyl-1-pyrroline by an improved and novel method from proline.
DETAILED DESCRIPTION OF THE INVENTION
In accordance to the objectives, the present invention provides a process for the preparation of 2-acetyl-1-proline
Gurudutt Kambadoor Nagarajarao
Srinivas Pullabhatia
Arent & Fox PLLC
Chesser Wilburn L.
Council of Scientific and Industrial Research
Powers Fiona T.
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