Хімія та хімічні технології/ 6. Органічна хімія

O. I. Panasenko, V. P. Buryak, A. S. Gotsulya, A. A. Safonov, N. A. Postol

Zaporozhye State Medical University

NIPHEDIPINE AND AMLODIPINE IDENTIFICATION IN ACCORDANCE WITH ITS OPTICAL CHARACTERISTICS OF THEIR ELECTRONIC BANDS ABSORPTION

Drugs dandification in accordance with the requirements of modern pharmacopoeia analysis [1-7] carried out as by a chemical method, as by means of the optical characteristics of the electronic bands of the maximum UV-spectrum absorption-position (λ_max , nm) of the specific absorption rate (and molar extinction coefficient (). However, in the case of similar in structure compounds, an applying of these recommendations is a little tricky.

On the example of two drugs, 1,4-dihydropyridine derivatives, we proved the possibility of using one of the methods of mathematical statistics - method of the relative dispersions comparison for the informational-retrieval system developing for the compounds identification, using the following absorption spectra parameters as a half-width absorption band, the ascylyrator strength, integrated intensity and matrix element of the electrons transition (OOXECB).

Amlodipine Niphedipine

Materials and research methods. For studying of the absorption UV-spectra were used amodipine and niphedipine standard samples, which we had received from the State enterprise "Scientific-expert pharmacopoeia centre" Kharkov. As the solvent was used 95% ethanol, which corresponds to the requirements of the State Pharmacopoeia of Ukraine. Amlodipine and niphedipine UV-spectra were measured by means of the spectrophotometer Shimadzu UV 1800 in quartz cuvettes with a layer thickness 10 mm.

Logical identification. Taking into account the fact that the accuracy of the wavelength determination is very high (± 0,5 nm) and knowing the number of peaks and also their corresponding values, it would seem, that by a logical way it is possible to identify the research drugs that are close to each other in their chemical structure and therefore have similar absorption spectra. Our researched drugs amlodipine and nifedipine cannot be recognized by logical way.

Knowing that in the world medical practice using more than 12,000 individual compounds, undoubtedly, there are many drugs that have similar UV-spectra, and the difference in their values, and situated within the spectrophotometer error. We decided to create an informational-search system for possible automation of the method of drugs identification based on the use of an additional optical characteristic: the half-width of the absorption band (∆ν_1̸2), ascylyrator strength (f), the integrated intensity (A) and electron transfer matrix element (MIC).

Statistical method of drugs identification by OOXECB. Assume first that the medicines that we identified relate to a group of 1,4-dihydropyridine derivatives (table 1). The concentration of researched solutions of drugs in all cases 1 mg % in ethanol.

Table 1

Optical characteristics of electronic absorption spectra of amlodipine (1) and niphedipine (2)

Substance	λ, nm	V, cm^-1	ε·	lg·ε	∆ν1̸2	A·	f	Мік·
1.	241	41500	1,56	4,19	5280	0,90	0,99	3,60
2.	243	41200	1,54	4,15	4980	0,88	0,96	3,54

In our case we have a matrix consisting of m rows (m - number of drugs, among which cannot be identified the unknown compound by logical analysis method) and n - column (n - amount taken into account by OOXECB). And, further, we have the vector-row consists of n OOXECB of the unknown drug. The problem consists in the identification of a substance, i.e., in its relation to one of the m unknown substances. Estimated OOXECB are averages from six parallel measurements.

Successful application of the method of dispersion's comparison is possible in the case of independent random quantities that are distributed by normally law. Based on this condition, it is necessary from the optical characteristics of the electronic absorption spectra exclude a wave number (ν_max) and, because they are functionally connected with the values λ_max and E_max.

Other characteristics may be taken into account in the first approximate independent, despite the fact that between some of them there is a correlation connection.

In order to exclude the influence of the dimension, it is necessary to consider instead of the optical characteristics of the electronic spectra their water bearing values:

; ; ; ; ;; (1),

where marked with a star optical characteristics of electronic spectra of an unknown drug, and at the denominator's ratio are presented OOXECB of each from the "theoretically" known drugs. We calculate the squared of deviations of these indicated relative values from the unity, i.e. (/, (/,… (/ (2).

Sum of squared deviations per unit amounts taken into account optical characteristics (n-1 = 6-1 = 5) will be present an unbiased assessment of relative values (then used "relative dispersion")

(/, (/,… (/ (3)

The minimum sum amount for any of the same drug will testify about: namely i-th is a drug, is the fact, that we are looking for: . If it is necessary to get a statistically significant conclusion is that the i-th drug is the fact that we are looking for, it is necessary to compare the relative dispersion with other the nearest by its value dispersion for a drug. Firstly, calculate the dispersion correlation:

(4)

The number of freedom degrees for this correlation in our case equals to . If it is , so it is more likely (more than 90%) i-th drug is the drug that we identify. For a more accurate probability can be used a K. Branuli statistical theory.

For drugs that are the calcium channel blockers, at first glance it seems that it is not possible to identify an unknown substance with more than two drugs. However, the identification practice indicates that for this group of medications cannot be presented more than two tested compounds which are not amenable to identification.

In our case, a statistical method that is considering, allows accurately enough to identify an unknown substance.

Identification algorithm of derivatives of 4,4-dihydro-pyridine by OOHESV. Denote through the optical characteristics of the electronic absorption spectra; ε; , . Mik of i-th drug substance (i = 1, 2 ... m; for indicated in table 1 pair of drugs with m = 2).

OOHESV of the unknown medical substance through

By comparing the optical properties of an unknown drug with optical characteristics of electronic absorption spectra of each from i-th drugs, we obtain n values of the relative dispersions by formula:

 (5).

Then we performed a search of the minimal value of the relative dispersions in size from the smallest to the largest value:

The second, bigger by its quantity relative dispersion after mark . Calculation of the dispersion correlation performs using the formula 4 (). During a comparison of the dispersion correlation with critical values , if , then, i-th drug is our searching compound. If it is necessary, repeat measurements.

An example of drug identification

X₁^* = 242; x₂^* = 2,03·10⁴; x₃^* = 5,32·10³; x₄^* = 1,10·10⁸; x₅^* = 1,18; x₆^* = 4,72·10^-18.

It is known that our searching substance refers to medicines - 1,4-dihydropyridine derivatives.

In table 2 entered indicated values OOHESV of the unknown drug and theoretical optical characteristics of electronic spectra of two researched drugs (table 1). Table 2 shows all calculations of the relative dispersions. As the calculation results show, the lowest value of relative dispersion S_i² = 18,94·10⁴ is obtained by comparing an unknown medical substance with niphedipine. The next relative dispersion equals to 35,98, compared with amlodipine.

The dispersion corellation and is more amount . Therefore, with more relativity, in accordance with normal distribution law by K. Browne with a probability more than 90% we could consider that our unknown substance is amlodipine.

For drugs identification by the basic optical characteristics of electronic absorption bands by means of a computer, is compiled programs algorithm (table 2).

Table 2

Identification of an unknown compound (1), from the group of calcium, amlodipine (2) and nifedipine (3) antagonists

Substance	Symbol				Xi4=A·10^8
1	2	3	4	5	6	7	8	9	10
1		242	1,49·	8660	1,30	1,42	5,08	-	-
2		241 0,172	1,56· 20,13	5280 4,098	0,90 1,975	0,99 1886	3,60 1,690	- 9669	- 1934
3		243 0,169	1,54· 24,30	4,980 24,70	0,88 23,41	0,96 19,46	3,54 24,59	- 116,6	- 23,32

For medicinal substances, a calcium antagonist at first it seems that it is impossible to identify an unknown substance with more than two drugs. However, the identification practice shows that for this group of drugs more than two drugs cannot be among the test compounds which cannot be identified.

CONCLUSIONS

1. It is established that the values of half-width ∆ν_1̸2 and integral intensity of A absorption bands, oscillator strength f and the electrons transition matrix Mik element can be use as important constants of medicines for their identification.

2. The values A, f and Mik could serve as characteristic constants for 1,4-dihydropyridine derivative side identification, because they differ for individual substances on 90%.

3. By the integral intensity quantities, oscillator strength and the electrons transition matrix element for test substances, such a row: amlodipinniphedipin.

4. Created the algorithm of a program for personal computers for drugs identification, summing the optical properties of their electronic absorption spectra (A, f, Mik), which can be realized by means of computer.

LITERATURE

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