Digest Journal of Nanomaterials and Biostructures Vol. 9, No. 1, January - March 2014, p. 433 - 442 IN VITRO ANTIMICROBIAL ACTIVITY OF SOME NEWLY SYNTHESIZED POLYPEPTIDE CANDIDATES A. M. NAGLAH a,b* , N. M. KHALIFA a,c , M. A. AL-OMAR a , H.M. AWAD d , ABD EL-GALIL E. AMR a,e a Pharmaceutical Chemistry Department, Drug Exploration & Development Chair,College of Pharmacy, King Saud University,Riyadh 11451, Saudi Arabia b Peptide Chemistry Department, Chemical Industries Research Division, National Research Centre, 12622-Dokki, Cairo, Egypt c Theripeutical Chemistry Department, National Research Centre, 12622- Dokki, Cairo, Egypt d Chemistry of Natural and Microbial Products Dept., Pharmaceutical Industries Div., NationalResearch Centre, 12622-Dokki, Cairo, Egypt e Applied Organic Chemistry Department, National Research Centre, 12622- Dokki, Cairo, Egypt Antimicrobial peptides (AMPs) have been tested with respect to their possible application as chemotherapeutic agents. The current study aimed to synthesize and evaluate the potential antimicrobial activity of new peptide chains.These compounds were prepared by the liquid phase method loaded on polyethylene glycol as apolymeric support. The compounds were fully characterized by spectral data. The in vitro antimicrobial activity of the synthesized peptides was screened against Gram-positive (Bacillus subtilits) and Gram-negative (Escherichia coli) bacteria, yeast (Candida albicans) and filamentous fungi (Aspergillusniger). The results of biological activity were interpreted and discussed. (Received January 13, 2014; Accepted March 31, 2014) Keywords: Antimicrobial; Liquid Phase Method; Polypeptides; Polyethylene Glycol 1. Introduction Since the introduction of the Merrifield method for peptide synthesis [1], insoluble polymer supports have been incorporated into numerous synthetic methodologies to facilitate product purification [2]. Although highly successful, solid-phase synthesis still exhibits several shortcomings due to the nature of heterogeneous reaction conditions [3]. By replacing insoluble cross-linked resins with soluble polymer supports, the familiar reaction conditions of classical organic chemistry are reinstated, and yet product purification is still facilitated through application of macromolecular properties [4]. This methodology, termed liquid-phase peptide synthesis, in essence avoids the difficulties of solid-phase synthesis while preserving its positive aspects [5]. Soluble polymer that has been used in liquid phase synthesis is polyethylene glycol that is an uncharged, hydrophilic polymer, which is soluble in water as well as in most organic solvents and insoluble in hexane, diethyl ether [6]. Furthermore, the solubilizing power of PEG not only allows homogeneous reactions under numerous reaction conditions, but these solubility properties permit individual reactions steps to be monitored without requiring cleavage of product from the polymer support [7]. The characterization of PEG-bound organic moieties is often straightforward as the polymer does not interfere with spectroscopic or chemical methods of analysis; additionally [8]. Due to its low toxicity and immunogenicity, PEG is highly suitable for biomedical * Corresponding author: amnaglah@gmail.com