Introduction. A modification of known drugs is one of the main tools of medicinal
chemistry. Monastrol (ethyl 4- (3- hydroxyphenyl)- 6- methyl- 2- thioxo- 1,2,3,4-tetrahydropyrimidine-
5- carboxylate) (1) is a multifunctional compound and exhibits high biological activity
[1].
Purpose of the study. The presence of functional groups in the molecule allows for various
chemical modifications.
Materials and methods. In order to obtain new derivative (2), it was suggested to carry out
the cyclization of Monastrol with acetoacetic ester in the presence of sulfuric acid under the
conditions of Pechmann reaction with possible cyclization over the phenolic group [2]. The
cyclization has occurred in an unexpected manner: it involved the sulfur and the nitrogen atoms as
well.
Results and discussion. As a result of the reaction based on physic-chemical methods
(IR,1H, 15N -and 13C NMR) the product (3) was isolated which has been assigned the following
structure: ethyl 8-(3-hydroxyphenyl)-2,2,4,6-tetramethyl-2,6,7,8-tetrahydropyrimido [2,1-
b][1,3]thiazine-7-carboxylate (3) and ethyl6-(3-hydroxy phenyl)-2,2,4,8-tetramethyl-2,6-
dihydropyrimido[2,1-b][1,3]thiazine-7-carboxylate(4) in raport 1:3.
Conclusion. Аs a result of this experiment, we got two new substances with unusual
heterocyclization.

Picture 1 Heterocyclization of monastrol under the conditions of the Pechmann reaction
References.
1. C. Oliver Kappe, O. V. Shishkin, G. Uray, P. Verdino. Tetrahedron, 2000, 56, 1859-
1862.
2. Т.В. Шокол, Э.Н. Абдуллаев, Н.В. Горбуленко, М.С. Фрасинюк, В.П. Хиля. Хим.
Прир. Соед., 2018, 3, 373-376.