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Microbial surface attachment negatively impacts a wide range of devices from water purification membranes to biomedical implants. Mimics of antimicrobial peptides (AMPs) constituted from poly(N‐substituted glycine) „peptoids“ are of great interest as they resist proteolysis and can inhibit a wide spectrum of microbes. We investigate how terminal modification of a peptoid AMP‐mimic and its surface immobilization affect antimicrobial activity. We also demonstrate a convenient surface modification strategy for enabling alkyne–azide „click“ coupling on amino‐functionalized surfaces. Our results verified that the N‐ and C‐terminal peptoid structures are not required for antimicrobial activity. Moreover, our peptoid immobilization density and choice of PEG tether resulted in a „volumetric“ spatial separation between AMPs that, compared to past studies, enabled the highest AMP surface activity relative to bacterial attachment. Our analysis suggests the importance of spatial flexibility for membrane activity and that AMP separation may be a controlling parameter for optimizing surface anti‐biofouling., Efficient anti‐biofouling: We show that an archetypical antimicrobial peptoid could retain high activity even with terminal modifications. Immobilization by alkyne–azide „click“ coupling on one‐step modified amino‐surfaces was demonstrated. Appropriate spatial separation between immobilized peptoids, rather than increasing surface density, was found to promote both resistance against bacterial attachment and AMP surface activity.

The conjugation of photosensitisers to proteins or targeting peptides is a well-established approach for enhancing solubility and tissue selectivity for both photodynamic therapy (PDT) of cancer and light-activated drug delivery. A key innovation in the development of such targeted photosensitisers is the application of biorthogonal ligation techniques (e.g. azide-alkyne “click” chemistries) which allow the efficient attachment of various photosensitiser molecules to multifunctional peptides. Some of our work in this area will be described towards the generation of specific targeted conjugates between porphyrin and chlorin photosensitiser derivatives and tumour-homing or cell-penetrating peptide carriers [1, 2]. Conjugation of hydrophobic photosensitiser molecules to cationic cell-penetrating peptides (e.g. HIV Tat 48-57) can provide derivatives with improved water solubility, amphiphilicity, enhanced uptake and predictable sub-cellular localisation. This is very attractive for the light-triggered delivery of macromolecular therapeutics by photochemical internalisation (PCI), which will be illustrated in the application of these compounds for the delivery of the protein toxin, saporin [3]. Peptide targeting strategies are also of interest for PDT with 5-aminolevulinic acid (ALA) [4]. In ALA-PDT, administered ALA is converted within cells via the heme biosynthetic pathway to a classical photosensitiser- protoporphyrin IX. In this context, some recent chemical and biological data will be presented on the use of peptide targeting to enhance the delivery of multiple ALA units to a specific cell type [5]. [1] Dondi, R., Yaghini, E., Tewari, K. M., Wang, L., Giuntini, F., Loizidou, M., MacRobert, A. J. and Eggleston, I. M., Org. Biomol. Chem. 2016, 14, 11488-11501; [2] Yaghini, E., Dondi, R., Tewari, K. M., Loizidou, M., Eggleston, I. M. and MacRobert, A. J., Sci. Rep. 2017, 7, 6059; [3] Yaghini, E, Dondi, R., Edler, K. J., Loizidou, M., MacRobert, A. J. and Eggleston, I. M., Nanoscale 2018, 10, 20366-20376; [4] Tewari, K. M. and Eggleston, I. M., Photochem. Photobiol. Sci. 2018, 17, 1553-1572; [5] Tewari, K. M., Dondi, R., Yaghini, E., Pourzand, C., MacRobert, A. J. and Eggleston, I. M., Bioorg. Chem. 2021, 109, 104667.

Photodynamic therapy (PDT) is a promising approach for the targeted treatment of cancer and various other human disorders. An effective, clinically approved approach in PDT involves the administration of 5-aminolevulinic acid (ALA) to generate elevated levels of the natural photosensitiser protoporphyrin IX (PpIX). The development of prodrugs of ALA is of considerable interest as a means to enhance the efficiency and cell selectivity of PpIX accumulation for PDT applications. In this work a novel peptide-targeted dendrimeric prodrug of 5-aminolevulinic acid (ALA) 13 was synthesised which displays nine copies of ALA on a core structure that is linked to a homing peptide for targeted delivery to a specific cancer cell type. The synthesis was accomplished effectively via a flexible, modular solid phase and solution phase route, using a combination of solid phase peptide synthesis and copper-catalysed azide-alkyne cycloaddition chemistry. The prodrug system shows a sustained and enhanced production of protoporphyrin IX (PpIX) in the MDA-MB-231 cell line that over-expresses the epidernal growth factor receptor (EGFR+) in comparison to equimolar ALA and the corresponding non-targeted ALA dendrimer (nine copies of ALA). This study provides a proof of concept for the development of a new generation of prodrugs for ALA-based photodynamic therapy that can deliver an enhanced ALA payload to specific tissue types.

It has come to our attention that some of our cryo-electron microscopy (cryo-EM) images actually show ice contamination, (1) instead of the soft matter aggregates originally indicated in our publication. The images only relate to counterexample peptoid sequences that did not properly assemble (originally Figures 3D–K and S5E–G, I–M, and P). As such, our main finding of an ultrashort water-soluble tripeptoid assembling into ordered nanofibers is not changed. Our overall conclusions based on complementary cryo-EM, DLS, CAC, and fluorescence spectroscopy measurements are also unaffected. Nonetheless, the figures indicated and associated text require correction. In re-examining our cryo-EM data set, we found micrographs showing additional structures that are unlikely to be contaminants, which we previously took as less representative. Like the artifacts, the structures now identified are also irregular and consist of an ensemble of sizes centered around a mean. Incidentally, the mean sizes of these structures (50–250 nm in diameter, depending on sequence) fit better with our complementary DLS results—no agglomeration effect of individual 5–20 nm ice artifacts is needed anymore to reconcile the sizes measured by EM and DLS.

Peptoids are biofunctional N-substituted glycine peptidomimics. Their self-assembly is of fundamental interest because they demonstrate alternatives to conventional peptide structures based on backbone chirality and beta-sheet hydrogen bonding. The search for self-assembling, water-soluble "minimal" sequences, be they peptide or peptidomimic, is a further challenge. Such sequences are highly desired for their compatibility with biomacromolecules and convenient synthesis for broader application. We report the self-assembly of a set of trimeric, water-soluble α-peptoids that exhibit a relatively low critical aggregation concentration (CAC ∼0.3 wt %). Cryo-EM and angle-resolved DLS show different sequence-dependent morphologies, namely uniform ca. 6 nm wide nanofibers, sheets, and clusters of globular assemblies. Absorbance and fluorescence spectroscopies indicate unique phenyl environments for ?-interactions in the highly ordered nanofibers. Assembly of our peptoids takes place when the sequences are fully ionized, representing a departure from superficially similar amyloid-type hydrogen-bonded peptide nanostructures and expanding the horizons of assembly for sequence-specific bio- and biomimetic macromolecules.

The administration of 5-aminolevulinic acid (ALA) to generate enhanced intracellular levels of endogenous porphyrins is currently one of the most important approaches for photodynamic therapy (PDT) and photodiagnosis (PDD). Despite the great promise of ALA-based PDT, the physicochemical behaviour and chemical reactivity of ALA are problematic, and a variety of chemical approaches have been brought to bear to improve cellular delivery, enhance porphyrin production, and generate ALA prodrugs that have appropriate stability for convenient clinical use, as well as selectivity for cancerous tissues. While there has been considerable success, there are still a number of challenges to be addressed and opportunities to be exploited through application of chemical insight in this area.

Amphiphilic cell-penetrating peptide–porphyrin conjugates have been developed for application in light-based therapeutic techniques., Efficient syntheses of cell-penetrating peptide–porphyrin conjugates are described using a variety of bioconjugation chemistries. This provides a flexible means to convert essentially hydrophobic tetrapyrolle photosensitisers into amphiphilic derivatives which are well-suited for use in light-triggered drug delivery by photochemical internalisation (PCI) and targeted photodynamic therapy (PDT).

There is great interest in synthetic polymers that mimic the high degree of functionality observed in peptides and proteins. However, creating a peptidomimetic system that can be easily programmed to present complex structures, biological functions, and morphological features remains a challenge. Specific ordering of diverse monomers in specific sequences to simultaneously encode structural and biochemical functionalities is a hallmark of functional biopolymers. Poly( N -substituted glycines) “peptoids,” prepared using the step-wise solid phase synthesis, constitute a class of novel sequence-specific polymers with a unique combination of bioactivity, synthetic convenience, low immunogenicity, and resistance against proteolysis. Remarkably, these properties arise simply out of a one-atom position shift of the peptide side chain from the alpha-carbon to the amide nitrogen along the peptide backbone. This article reviews the progress in peptoid therapeutics as well as the recent efforts in applying peptoids as alternative materials to peptides and conventional polymers for the self-assembly of nanostructures and for biomedical applications.

Bioprecursor by definition is a type of prodrug that is designed to tackle pharmaceutical, pharmacokinetic or pharmacodynamic shortcomings of a drug that limit its clinical use. A retrometabolic approach is used to design bioprecursors which upon activation by either phase-I or phase-II metabolic enzymes result into an active metabolite. A bioprecursor differs from its active metabolite in many respects like physico-chemical, biological and toxicological aspects. Present review focuses on salient features of design and chemistry of bioprecursors and their active metabolites, activating metabolic enzymes/reactions, reported examples from literature and applications. We hope that this extensive compilation would open doors to bioprecursors and their active metabolites as very promising resources for the discovery of novel drugs possessing high efficacy with lower number and extent of adverse effects.

Apoptosis is a process, which involves a sequence of cellular changes, which ultimately lead to cell death. This programmed cell death is a normal phenomenon required for growth of an organism. Inhibition of apoptosis can result in a number of cancers, inflammatory and autoimmune diseases and viral infections. Inhibitors of apoptosis proteins (IAPs) are a family of structurally and functionally related proteins, which play a crucial role in apoptosis (programmed cell death), proliferation and angiogenesis. Till date 8 IAPs have been identified (Survivin, XIAP, Livin, cellular IAP 1 and 2, ILP-2, NAIP and BRUCE/Apollon). The current review discusses individual protein in details with respect to its structural features, functions and clinical significance. These proteins; especially survivin, XIAP and Livin have been found to express in wide range of malignancies and hence taken as a target of interest by various research groups. The review also highlights the various Phase- 1 and 2 studies of new therapeutic agents that are being developed either as a monotherapy or in combination with existent drugs, which target these IAPs.

Prodrug approach using diglyceride as a promoiety is a promising strategy to improve bioavailability of poorly absorbed drugs and the same was explored in the present work to improve oral bioavailability of norfloxacin; a second generation fluoroquinolone antibacterial. The prodrug was synthesized by standard procedures using dipalmitine as a carrier and the structure was confirmed by spectral analysis. Higher LogP indicated improved lipophilicity. The ester linkage between norfloxacin and dipalmitine would be susceptible to hydrolysis by lipases to release the parent drug and carrier in the body. In vivo kinetic studies in rats indicated 53% release of norfloxacin in plasma at the end of 8h. The prodrug exhibited improved pharmacological profile than the parent compound at equimolar dose that indirectly indicated improved bioavailability.