Introduction. Thryptanthrin (6,12-dihydro-6,12-dioxoindolo-(2,1-b)-
quinazoline) – natural alcaloid contained in various medicinal indigo plants (Isatis
indigotica, Strobilanthes cusia and others) was reported in numerous scientific papers
as antimicrobial, antiinflammatory, antitumor, antituberculous compound, etc. Based
on this results were synthesized many derivatives and structural analogues, which
reproduce partially or completely thryptanthrin structure and effects. One of these
compounds is thryptanthrin analogue (TA) – 2-(propylsulfanyl)-5H-
[1,3,4]thiadiazolo[2,3-b]quinazolin-5-one (Fig.1), synthesized by Macaev et al. in
2015, at the Institute of Chemistry (Academy of Sciences of Moldova), demonstrated
antituberculosis properties.

Fig.1 Structural formulas of thryptanthrin (left) and its synthetic analogue (right)
In attempt to amplify antituberculosiseffect of thryptanthrin analogue were
obtained solid binary systems with β-cyclodextrin (β-CD) – cyclic oligosaccharide
consisting of 7 glucopyranose units.
Aim. Study of intermolecular interactions between thryptanthrin analogue – 2-
(propylsulfanyl)-5H-[1,3,4]thiadiazolo[2,3-b]quinazolin-5-one and β-cyclodextrin.
Materials and methods. The following reagents were used: β-cyclodextrin,
molecular formula C42H70O35, molecular weight 1134.98, was purchased from Sigma;
2-(propylsulfanyl)-5H-[1,3,4]thiadiazolo[2,3-b]quinazolin-5-one, molecular formula
C12H11N3OS2, molecular weight 277.36, was synthesized and purified in our
laboratory.
FT-IR spectra of TA, β-CD and of binary systems were obtained using KBr
pellet technique and were colected with PerkinElmer spectrometer „Spectrum 100
FT-IR‖ in the 4000 to 650 cm-1 spectral range with the resolution of 1 cm-1.
Solid binary systems were obtained through kneading method: equimolar
amounts of β-CD and TA were weighed and passed in agate mortar. Obtained
mixtures were wetted with appropriate quantity of distilled water so as to obtain a paste. The paste was blended for 60 minutes once in a while adding water to keep paste consistency. Then it was milled for 30 minutes without addition of water. Obtained systems were stored in sealed with parafilm sample tubes, at room temperature (20±2°C).
Results and discussion. In order to study intermolecular interactions between β-CD and TA were colected IR spectra of individual compounds and of binary system (Fig.2).
Fig.2 IR spectra of β-CD, TA and binary systems (β-CD – TA)
As can be clearly seen, new bands not occur in binary system spectre, in comparison with TA and β-CD spectra. Occur shifts of binary system peaks comparing with: TA peaks positions (1463 (to 1455) cm-1, 1571 (to 1575) cm-1 and 1704 (to 1709)cm-1, corresponding to bending vibrations of ν[C-H], stretching vibrations of ν[C=C]aromatic and stretching vibrations of ν[C=O], respectively) and β-CD peak position (3265 (to 3300) cm-1 corresponding to stretching of ν[OH]). Also we can see changes in the intensities of some binary systems peaks (at 1027 cm-1 (bending vibration of ν[O–H]) – binary system peak intensity is higher than intensity of β-CD peak; at 1455, 1575, 1709 and 3300 cm-1 binary system peak intensity is lower than intensity of TA and β-CD peaks, respectively). Based on experimental and theoretical data in this area it can be assumed that β-CD interacts with TA through hydrogen bonds formed between the carbonyl functional groups of TA and hydroxyl groups of β-CD.
Conclusions. β-cyclodextrin interact with 2-(propylsulfanyl)-5H-[1,3,4]- thiadiazolo[2,3-b]quinazolin-5-one in the solid binary systems predominantly through hydrogen bonds.