Synthesis of N -acetyl and N -formyl pyrazoline derivatives from vanillin and their antigenotoxic activity

: Vanillin is one of the most important natural products, used as a starting material in the new drug design procedures. Starting from vanillin, we can prepare different chalcones, which are known for their pronounced pharmacological and biological activities. For this reason some chalcone analogues have been synthesized from the corresponding vanillin derivatives. Further reaction with hydrazine in formic acid or acetic acid yielded 20 new pyrazoline compounds with N -formyl and N -acetyl groups, respectively. All new compounds were well characterized by IR, 1 H and 13 C NMR spectroscopy and physical data. In vitro DNA protective potential of selected compounds on hydroxyl and peroxyl radical-induced DNA damage was investigated. The results showed that the new synthesized compounds had expressed potential to prevent DNA damage.


Introduction
Many natural products were used as starting materials in the new drug design, and vanillin is one of them. Different kinds of compounds, which are isolated from some natural products, have vanillin fragment as part of their structure. Presence of those compounds in plants are usually responsible for very well expressed medicinal properties and they have been used in some forms of traditional medicine treatments.
Some of them are:  dehydrozingerone-isolated from ginger,  capsaicin-active component of chili peppers,  piperine-isolated from black pepper,  curcumine-produced by Curcuma longa plants Dehydrozingerone is a well-known phenolic compound with a broad spectrum of biological activity. [1][2][3] It is the structural half analogue of curcumin, also exhibits an exhaustive range of activity such as antiinflammatory, antioxidative, antitumor, hypoglycaemic, hepatoprotective, antilipoperoxidation activity,… [4][5][6][7] An interesting feature of these two compounds is that they serves as starting materials for the synthesis a large number of different kinds of compounds. Enone system presented in both of them is the key part of substrates and could be easily transformed into various usable heterocyclic derivatives such as pyrimidines, 2-aminopyrimidines, pyrazolines, pyrazoles, oxazoles, thiazoles, isoxazoles, oxazines, thiazines, … Pyrazolines are extensive important synthons in the synthetic organic chemistry and drug designing.
In light of this, we supposed that vanillin is suitable substrate for further transformation. Alkylation/ allylation of the phenol group of the vanillin was achieved by a standard procedure 8-10 using an alkyl/allyl halide to yield the corresponding phenoxy compounds 1(a-j). Starting from our previous results in dehydrozingerone derivatives transformation 11,12 we decided to prepare some dehydrozingerone analogues, with rigid cyclopropane ring fragment instead of methyl one, in reaction O-alkyl vanillines and methyl cyclopropyl ketone. On this way, chalcone like compounds 2(a-j), (E)-1-cyclopropyl-3-(4-alkoxy-3methoxyphenyl)prop-2-en-1-ones were synthesized.
These enone compounds are very good starting point for different types of synthesis. In reaction with hydrazine hydrate in acidic solvent (boiling formic acid or acetic acid) obtained a series of novel N-formyl, 3(a-j) and N-acetyl, 4(a-j) pyrazoline derivatives in 69-98% yield.
All new products were characterized by their spectral data (IR, 1 H NMR and 13 C NMR).
In vitro DNA protective potential of compounds numbered from 3(a-j) to 4(a-j) were analysed using antioxidant assays. Whether selected compounds could protect against Fe 2+ , H 2 O 2 and AAPH-induced DNA damage Salmon sperm DNA was used as negative control while quercetin (100 μg/mL) was the reference compound.
The decreasing order in the reduction of DNA damage were found to be 3c = 3e > 3a = 4e > 3d = 3g = 4c > 4a > 3f = 3i = 4h > 4g = 4i (Таble 2). The protection against DNA damage induced with AAPH by 3g and 4g was dose-dependent, increasing with higher dosage. As well as in the previous assay the results indicated that the compound 4b and 4d possessed significantly less protective potential in relation to other compounds.

Conclusions
 Vaniliin, as an easily accessible natural product, was modified by the simple synthetic procedure. The vanillic core give us a opportunity to tune their structure and properties by changing O-alkyl group in p-position. The new dehydrozingerone analogues were prepared by Claisen-Schmidt reaction and reacted with hydrazine in boiling formic or acetic acid. By this way new N-formyl and N-acetyl pyrazoline derivatives were prepared. All described compounds were synthesized in fairly good yields.
 All compounds were characterized by their spectral data (IR and 1 H-and 13 C-NMR). In vitro DNA protective potential of selected compounds for DNA damage caused by hydroxyl and peroxyl radicals, were performed.
 These results showed that the eleven compounds, namely 3a, 3c, 3d, 3e, 3g, 3h, 4a, 4c, 4e, 4h and 4i, could protect DNA against oxidative damage and that further studies might be beneficial. Selected compounds will be evaluated as in vivo genotoxic agents in Wistar rat livers and kidneys using the comet assay. Compounds without genotoxic activity well be applied prior to ethyl methanesulfonate (EMS) to quantify potential antigenotoxic effect. Those compounds that will prevent EMS mutagenic effect can be applied in the cancer treatment to prevent the genotoxic effect of anticancer agents.