meto-Phenylene Ethynylenes (mPE)

meta-Phenylene ethynylenes (mPE) are hydrocarbon scaffolds composed of phenyl rings connected by ethynylene linkages at the meta position (Fig. 8.4) [13, 135]. mPEs can adopt either an extended conformation (trans) or a helical conformation (cis) (see Chapter 3) [135-138]. The conformation is dependent on solvent [135, 137] and the presence of hydrogen-bonding functionalities [138]. Biological activity has only been introduced into mPEs with an extended conformation [139]. mPEs composed of alternating cationic primary amines and nonpolar alkyl groups have been designed to adopt an extended all trans conformation. mPEs are amenable to large scale synthesis and are composed of inexpensive monomers. Various 3-alkoxy-substituted 1,3-diiodobenzenes carrying Boc-protected amines in the 5-position were readily obtained via Mitsunobu etherification, and polycon-densation with 1,3-diethynylbenzene under Sonogashira-Hagihara cross-coupling conditions followed by deprotection afforded facially amphiphilic mPEs [140, 141].

x(H2C) + R= -O-n-pentyl, n=20, x=1 vNH3 -H, n=20, x=2

x(H2C) + R= -O-n-pentyl, n=20, x=1 vNH3 -H, n=20, x=2

Fig. 8.4 A meta-phenylene ethynylene oligomer which adopts an extended (trans) conformation and demonstrates antimicrobial activity.

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