Synthesis and Biological Activities of Distamicin A Analogues

Distamycin A is a natural product possessing amide group and three Nmethyl pyrrole rings terminated with neutral formamide and positively charged propylamidinium. It has been discovered and investigated as DNA minor groove binder, it acts as anti bacterial agent. Distamycin A binds to the minor groove of doublestranded DNA at Adinine-Thymine rich regions by forming hydrogen bond and hydrophobic interaction. Terminal amidine group of molecule is basic and have positive charge, this serve the molecule to be attracted to negatively charged DNA phosphodiester backbone. DNA is changed when it is bind with distamycin A. This is recognized from the chemical structure of minor groove. Distamycin A analogues have been synthesized to increase its binding with minor groove. In this research a new distamycin A analogues were synthesized by changing N-terminal alkyl group which have lower molecular weight and higher lipophilicity than previous analogues . This will increase the binding with minor groove, and may increase biological activity as anti cancer, in addition to its anti bacterial activity. XIII We have synthesized five new analogues of Distamycin A in this research, the synthesized analogues were characterized by 1 HNMR, 13 C NMR and IR. Synthesized compounds were tested for antioxidant ,antibacterial and antifungal activities. According to antibacterial activities the most active one was N-(1-Methyl5-(2-(4-sulfamoyl-phenyl)-ethylcarbamoyl)-1H-pyrrol-3-yl)-nicotinamide and Methanesulfonic acid 4-(2-((4-benzoylamino-1-methyl-1H-pyrrole-2carbonyl)amino)-ethyl)-phynel ester. They reveled about 10% of Gentamicin, whihl 4-benzoylamino-1-methyl-1H-pyrrole-2-carboxylic acid (3-dimethylamino-propyl)-amide revealed the highest activity against Microsproum Canis (72% inhibition). Fig (1): distamycin A structure. 1 Chapter One Introduction 1.1 Distamycin A Distamycin A is a natural antibiotic product with anticancer activity discovered in 1964. It was isolated from Bacterium Streptomyces Distallicus [1]. Distamycin A is one of the most extensively studied compounds which can bind reversibly in the minor groove of duplex DNA, by hydrogen bonds, Vander Waals contacts and electrostatic interactions, with high specificity for regions containing Adinine-Thymine (A-T) nitrogen base pairs [2]. Distamycin A acts as antibiotic with anticancer activity but it is too toxic to find application in cancer therapy[3]. It exhibits a high binding specificity and inhibits selectively initiation of transcription directed by certain prokaryotic promoters. Distamycin A displays antiviral and antibiotic activity, and active against gram-positive and gram-negative bacteria [3]. It shows antiprotozoal activity, which related to the ability of binding reversibly to the minor groove of DNA with a high selectivity for T-A rich sequences. At the cellular level, studies on Distamycin A show that, it inhibits the pathogenesis of functional complex formation at the promoter, by activating transcription initiation, and re-complex , box binding protine (TBP) and basal in vitro transcription[4]. There are other compounds like Distamycin A that have similar properties such as Netropsin. 2 Due to those reasons many of distamycin A analogues and conjugates have been synthesized. 1.2. Distamycin A Structure and Binding Distamycin A is oligopeptide constructed from 4-amino-l-methyl pyrrole acid moieties and strong basic side chain possessing isohelical shape to minor groove of DNA. The chemical structure of Distamycin A characterized by chain of three N-methyl pyrrole rings interconnected through with neutral formamide and positively charged propylamidinium Figure (1.1) [5]. Figure (1.1): Structure of Distamycin A. Distamycin A -like minor groove binders reach the cell nucleus hardly because of their poor membrane permeability[6]. The manner by which Distamycin A binds to DNA has inspired the various search for compounds with similar mode of action; some of these are being tested in clinical trials [7]. The binding of Distamycin A with minor groove takes place due to favorable Vander Waals interactions between C-H's of DNA minor groove along with hydrogen bond formation between NH groups of the pyrrole 3 carboxamide ring complex which stabilized negatively charged phosphate backbone binding of Distamycin A to DNA minor groove, widens the minor groove by unbending the helix axis and increases its length by nearly at cellular level [8]. The topology of the groove can be considered a smooth curve, however introducing a Guanine-Cytocin (G-C) nitrogen base pair with the exocyclic N-2 of guanine which points up into the groove causing a steric hindrance (clash) with the proton on C-3 of the pyrrole rings, this preventing the essential hydrogen bonds from being formed. So that the effective hydrogen bonds are possible in A-T regions ,Figure (1.2). Two Distamycin A molecules can be packed in minor groove with peptide group of one drug molecule stacked on the aromatic ring of the other. Anti-parallel hairpin motifs containing different sequences of N-methyl pyrrole and N-methylimidazole residues can recognize the broad category of nucleotide sequences in the minor groove . It has been reported that two parallel oligopyrrole carboxamide strands can be sandwiched in the minor groove of DNA[9].