Nonimmunogenic Hydrogel-Mediated Delivery of Antibiotics Outperforms Clinically Used Formulations in Mitigating Wound Infections.

Treatment of chronic wound infections caused by Gram-positive bacteria such as Staphylococcus aureus is highly challenging due to the low efficacy of existing formulations, thereby leading to drug resistance. Herein, we present the synthesis of a nonimmunogenic cholic acid-glycine-glycine conjugate (A6) that self-assembles into a supramolecular viscoelastic hydrogel (A6 gel) suitable for topical applications. The A6 hydrogel can entrap different antibiotics with high efficacy without compromising its viscoelastic behavior. Activities against different bacterial species using a disc diffusion assay demonstrated the antimicrobial effect of the ciprofloxacin-loaded A6 hydrogel (CPF-Gel). Immune profiling and gene expression studies after the application of the A6 gel to mice confirmed its nonimmunogenic nature to host tissues. We further demonstrated that topical application of CPF-Gel clears S. aureus-mediated wound infections more effectively than clinically used formulations. Therefore, cholic acid-derived hydrogels are an efficacious matrix for topical delivery of antibiotics and should be explored further.

Deciphering the Role of Intramolecular Networking in Cholic Acid-Peptide Conjugates on the Lipopolysaccharide Surface in Combating Gram-Negative Bacterial Infections.

The presence of lipopolysaccharide and emergence of drug resistance make the treatment of Gram-negative bacterial infections highly challenging. Herein, we present the synthesis and antibacterial activities of cholic acid-peptide conjugates (CAPs), demonstrating that valine-glycine dipeptide-derived CAP 3 is the most effective antimicrobial. Molecular dynamics simulations and structural analysis revealed that a precise intramolecular network of CAP 3 is maintained in the form of evolving edges, suggesting intramolecular connectivity. Further, we found high conformational rigidity in CAP 3 that confers maximum perturbations in bacterial membranes relative to other small molecules. Interestingly, CAP 3-coated catheters did not allow the formation of biofilms in mice, and treatment of wound infections with CAP 3 was able to clear the bacterial infection. Our results demonstrate that molecular conformation and internal connectivity are critical parameters to describe the antimicrobial nature of compounds, and the analysis presented here may serve as a general principle for the design of future antimicrobials.

Chloro-formyl steroids as precursors for hybrid heterosteroids: synthesis, spectroscopic characterization, and molecular and supramolecular structures.

Two new functionalized steroids containing both chloro and formyl substituents in ring A, and intended as precursors for the synthesis of hybrid systems, have been synthesized from ketosteroid precursors. 3-Chloro-2-formyl-17,17-dimethyl-18-nor-5α-androstane-2,13-diene, (I), and methyl 3-chloro-4-formyl-12-oxo-5ß-cholan-3-ene-24-oate, C26H37ClO4, (IV), have been synthesized using Vilsmeier reactions with 17ß-hydroxy-17α-methyl-5α-androstan-3-one and methyl 3,13-dioxo-5ß-cholan-24-oate, respectively. These products have been fully characterized using IR spectroscopy, 1H and 13C NMR spectroscopy, and high-resolution mass spectrometry, and in the case of (IV), a single-crystal X-ray diffraction study. Crystal structures have also been determined for the known analogues 3-chloro-2-formyl-17-oxo-5α-androst-2-ene, C20H27ClO2, (II), 3-chloro-2-formyl-5α-cholest-2-ene, C28H45ClO, (III), and the absolute and relative configurations are assigned for all four compounds (I)-(IV): when the fusion between rings A and B is trans, 3-chloro-2-formyl products are formed, but when this ring fusion is cis, a 3-chloro-4-formyl product results. The formation of (I) involves not only chloroformylation at ring A, but also dehydration and the 1,2 migration of a methyl group at ring D. In each of (II), (III) and (IV), rings B and C adopt almost perfect chair conformations, while ring A adopts a half-chair conformation. Ring D adopts an envelope conformation in each of (II) and (III), albeit differently folded in the two compounds, while in (IV), it adopts a half-chair conformation. A single C-H...O hydrogen bond links the molecules of (II) into C(6) chains which are linked into sheets by means of carbonyl-carbonyl interactions. The molecules of (IV) are linked into simple C(7) chains, again by a single C-H...O hydrogen bond, but there are no direction-specific interactions in (III) that are structurally significant.

Synthesis of 3ß-tert-Butyldimethylsiloxy-22-phenylthio-23,24-bisnorchola-5,9(11)-diene and Reductive Nucleophilic Attack on a Branched Aliphatic Aldehyde.

3ß-tert-Butyldimethylsiloxy-22-phenylthio-23,24-bisnorchola-5,9(11)-diene, which has a double bond between C-9 and C-11 and a phenylsulfenyl group on the terminus of the side chain, is a potential synthetic intermediate for steroids with 9,11-unsaturation or 9,11-seco skeletons. We describe here the synthesis of the title compound from 17-ethylenedioxy-3-acetoxyandrosta-3,5-dien-11-one. The introduction of an ethylene unit to 3ß-tert-butyldimethylsiloxyandrosta-5,9(11)-dien-17-one by the action of ethyltriphenylphosphonium bromide under basic conditions resulted in an inseparable mixture of two stereoisomeric products (5 : 1). However, in the subsequent step, only the (Z)-isomer was susceptible to the Lewis acid-catalyzed ene reaction with formaldehyde, giving a stereochemically pure product with the desired configuration. Within three steps, the ene-product was derivatized to the title compound, with a total yield of 53% over seven steps. Reductive terminal anion formation by treatment with lithium di-tert-butylbiphenyl (LiDBB) and subsequent nucleophilic attack on a branched aliphatic aldehyde was demonstrated, with an eye toward the introduction of side chains, especially for steroids with oxygen functionality at C-23.

Synthesis and activity evaluation of a series of cholanamides as modulators of the liver X receptors.

The Liver X receptors (LXRs) are members of the nuclear receptor family, that play fundamental roles in cholesterol transport, lipid metabolism and modulation of inflammatory responses. In recent years, the synthetic steroid N,N-dimethyl-3ß-hydroxycholenamide (DMHCA) arised as a promising LXR ligand. This compound was able to dissociate certain beneficial LXRs effects from those undesirable ones involved in triglyceride metabolism. Here, we synthetized a series of DMHCA analogues with different modifications in the steroidal nucleus involving the A/B ring fusion, that generate changes in the overall conformation of the steroid. The LXRα and LXRß activity of these analogues was evaluated by using a luciferase reporter assay in BHK21 cells. Compounds were tested in both the agonist and antagonist modes. Results indicated that the agonist/antagonist profile is dependent on the steroid configuration at the A/B ring junction. Notably, in contrast to DMHCA, the amide derived from lithocholic acid (2) with an A/B cis configuration and its 6,19-epoxy analogue 4 behaved as LXRα selective agonists, while the 2,19-epoxy analogues with an A/B trans configuration were antagonists of both isoforms. The binding mode of the analogues to both LXR isoforms was assessed by using 50 ns molecular dynamics (MD) simulations. Results revealed conformational differences between LXRα- and LXRß-ligand complexes, mainly in the hydrogen bonding network that involves the C-3 hydroxyl. Overall, these results indicate that the synthetized DMHCA analogues could be interesting candidates for a therapeutic modulation of the LXRs.

New cholic acid derivatives: Biocatalytic synthesis and molecular docking study.

A series of cholic acid derivatives was synthesized by enzyme catalysis. Eleven acetyl and ester derivatives of cholic acid, eight of them new compounds, were obtained through regioselective lipase-catalyzed reactions in very good to excellent yield. The influence of various reaction parameters in the enzymatic esterification, acetylation and alcoholysis reactions, such as enzyme source, alcohol or acylating agent: substrate ratio, enzyme: substrate ratio, solvent and temperature, was studied. Moreover, in order to shed light to cholic acid behavior in the enzymatic reactions, molecular docking of the lipase with cholic acid and some derivatives was carried out.

Insights on FXR selective modulation. Speculation on bile acid chemical space in the discovery of potent and selective agonists.

Bile acids are the endogenous modulators of the nuclear receptor FXR and the membrane receptor GPBAR1. FXR represents a promising pharmacological target for the treatment of cholestatic liver disorders. Currently available semisynthetic bile acid derivatives cover the same chemical space of bile acids and therefore they are poorly selective toward BA receptors, increasing patient risk for adverse side effects. In this report, we have investigated around the structure of CDCA describing the synthesis and the in vitro and in vivo pharmacological characterization of a novel family of compounds modified on the steroidal tetracyclic core and on the side chain. Pharmacological characterization resulted in the identification of several potent and selective FXR agonists. These novel agents might add utility in the treatment of cholestatic disorders by potentially mitigating side effects linked to unwanted activation of GPBAR1.

Gd-AAZTA-MADEC, an improved blood pool agent for DCE-MRI studies on mice on 1 T scanners.

A novel MRI blood-pool contrast agent (Gd-AAZTA-MADEC) has been compared with established blood pool agents for tumor contrast enhanced images and angiography. Synthesis, relaxometric properties, albumin binding affinity and pharmacokinetic profiles are reported. For in vivo studies, angiographic images and tumor contrast enhanced images were acquired on mice with benchtop 1T-MRI scanners and compared with MS-325, B22956/1 and B25716/1. The design of this contrast agent involved the elongation of the spacer between the targeting deoxycholic acid moiety and the Gd-AAZTA imaging reporting unit that drastically changed either the binding affinity to albumin (KA(HSA) = 8.3 × 10(5) M(-1)) and the hydration state of the Gd ion (q = 2) in comparison to the recently reported B25716/1. The very markedly high binding affinity towards mouse and human serum albumins resulted in peculiar pharmacokinetics and relaxometric properties. The NMRD profiles clearly indicated that maximum efficiency is attainable at magnetic field strength of 1 T. In vivo studies showed high enhancement of the vasculature and a prolonged accumulation inside tumor. The herein reported pre-clinical imaging studies show that a great benefit arises from the combination of a benchtop MRI scanner operating at 1 T and the albumin-binding Gd-AAZTA-MADEC complex, for pursuing enhanced angiography and improved characterization of tumor vascular microenvironment.

Synthesis and structure-activity relationships of amino acid conjugates of cholanic acid as antagonists of the EphA2 receptor.

The Eph-ephrin system plays a critical role in tumor growth and vascular functions during carcinogenesis. We had previously identified cholanic acid as a competitive and reversible EphA2 antagonist able to disrupt EphA2-ephrinA1 interaction and to inhibit EphA2 activation in prostate cancer cells. Herein, we report the synthesis and biological evaluation of a set of cholanic acid derivatives obtained by conjugation of its carboxyl group with a panel of naturally occurring amino acids with the aim to improve EphA2 receptor inhibition. Structure-activity relationships indicate that conjugation of cholanic acid with linear amino acids of small size leads to effective EphA2 antagonists whereas the introduction of aromatic amino acids reduces the potency in displacement studies. The b-alanine derivative 4 was able to disrupt EphA2-ephrinA1 interaction in the micromolar range and to dose-dependently inhibit EphA2 activation on PC3 cells. These findings may help the design of novel EphA2 antagonists active on cancer cell lines.

Calcium- and voltage-gated potassium (BK) channel activators in the 5ß-cholanic acid-3α-ol analogue series with modifications in the lateral chain.

Large conductance, calcium- and voltage-gated potassium (BK) channels regulate various physiological processes and represent an attractive target for drug discovery. Numerous BK channel activators are available. However, these agents usually interact with the ubiquitously distributed channel-forming subunit and thus cannot selectively target a particular tissue. We performed a structure-activity relationship study of lithocholic acid (LCA), a cholane that activates BK channels via the accessory BK ß1 subunit. The latter protein is highly abundant in smooth muscle but scarce in most other tissues. Modifications to the LCA lateral chain length and functional group yielded two novel smooth muscle BK channel activators in which the substituent at C24 has a small volume and a net negative charge. Our data provide detailed structural information that will be useful to advance a pharmacophore in search of ß1 subunit-selective BK channel activators. These compounds are expected to evoke smooth muscle relaxation, which would be beneficial in the pharmacotherapy of prevalent human disorders associated with increased smooth muscle contraction, such as systemic hypertension, cerebral or coronary vasospasm, bronchial asthma, bladder hyperactivity, and erectile dysfunction.

Structure-activity relationships and mechanism of action of Eph-ephrin antagonists: interaction of cholanic acid with the EphA2 receptor.

The Eph-ephrin system, including the EphA2 receptor and the ephrinA1 ligand, plays a critical role in tumor and vascular functions during carcinogenesis. We previously identified (3α,5ß)-3-hydroxycholan-24-oic acid (lithocholic acid) as an Eph-ephrin antagonist that is able to inhibit EphA2 receptor activation; it is therefore potentially useful as a novel EphA2 receptor-targeting agent. Herein we explore the structure-activity relationships of a focused set of lithocholic acid derivatives based on molecular modeling investigations and displacement binding assays. Our exploration shows that while the 3-α-hydroxy group of lithocholic acid has a negligible role in recognition of the EphA2 receptor, its carboxylate group is critical for disrupting the binding of ephrinA1 to EphA2. As a result of our investigation, we identified (5ß)-cholan-24-oic acid (cholanic acid) as a novel compound that competitively inhibits the EphA2-ephrinA1 interaction with higher potency than lithocholic acid. Surface plasmon resonance analysis indicates that cholanic acid binds specifically and reversibly to the ligand binding domain of EphA2, with a steady-state dissociation constant (K(D) ) in the low micromolar range. Furthermore, cholanic acid blocks the phosphorylation of EphA2 as well as cell retraction and rounding in PC3 prostate cancer cells, two effects that depend on EphA2 activation by the ephrinA1 ligand. These findings suggest that cholanic acid can be used as a template structure for the design of effective EphA2 antagonists, and may have potential impact in the elucidation of the role played by this receptor in pathological conditions.

[N-methyl-11C]cholylsarcosine, a novel bile acid tracer for PET/CT of hepatic excretory function: radiosynthesis and proof-of-concept studies in pigs.

UNLABELLED: Excretion of conjugated bile acids into bile is an essential function of the liver, and impairment of canalicular bile acid secretion leads to cholestatic liver injury. However, hepatic excretory function cannot be quantified in vivo because of the lack of suitable methods. Cholylsarcosine is an analog of the endogenous bile acid conjugate cholylglycine and exhibits characteristics in vivo that led us to hypothesize that the (11)C-labeled form, that is, [N-methyl-(11)C]cholylsarcosine ((11)C-cholylsarcosine), would be a suitable PET tracer for quantification of hepatic excretory function. METHODS: A method for radiosynthesis of (11)C-cholylsarcosine was developed involving (11)C-methylation of glycine followed by conjugation with cholic acid. Blood-to-liver uptake and liver-to-bile excretion were investigated in vivo by dynamic (11)C-cholylsarcosine PET/CT of 2 anesthetized pigs. In pig 1, a second dynamic (11)C-cholylsarcosine PET/CT examination was preceded by a high dose of the endogenous bile acid conjugate cholyltaurine to investigate possible inhibition of the transhepatocellular transport of (11)C-cholylsarcosine. In pig 2, a second (11)C-cholylsarcosine administration was given to determine the biodistribution of the tracer by means of 5 successive whole-body PET/CT recordings. Possible formation of (11)C-metabolites was investigated by analysis of blood and bile samples from a third pig. RESULTS: The radiochemical yield was 13% ± 3% (n = 7, decay-corrected) and up to 1.1 GBq of (11)C-cholylsarcosine was produced with a radiochemical purity greater than 99%. PET/CT studies showed rapid blood-to-liver uptake and liver-to-bile excretion of (11)C-cholylsarcosine, with radioactivity concentrations being more than 90 times higher in the bile ducts than in liver tissue. Cholyltaurine inhibited the transhepatocellular transport of (11)C-cholylsarcosine, indicating that the tracer is transported by one or more of the same hepatic transporters as cholyltaurine. (11)C-cholylsarcosine underwent an enterohepatic circulation and reappeared in liver tissue and bile ducts after approximately 70 min. There were no detectable (11)C-metabolites in the plasma or bile samples, indicating that the novel conjugated bile acid (11)C-cholylsarcosine was not metabolized in the liver or in the intestines. The effective absorbed dose of (11)C-cholylsarcosine was 4.4 µSv/MBq. CONCLUSION: We have synthesized a novel conjugated bile acid analog, (11)C-cholylsarcosine, and PET/CT studies on anesthetized pigs showed that the hepatic handling of tracer uptake from blood and excretion into the bile was comparable to that for the endogenous bile acid cholyltaurine. This tracer may be valuable for future studies of normal and pathologic hepatic excretory functions in humans.

Synthesis and olfactory activity of unnatural, sulfated 5ß-bile acid derivatives in the sea lamprey (Petromyzon marinus).

A variety of unnatural bile acid derivatives (9a-9f) was synthesized and used to examine the specificity with which the sea lamprey (Petromyzon marinus) olfactory system detects these compounds. These compounds are analogs of petromyzonol sulfate (PS, 1), a component of the sea lamprey migratory pheromone. Both the stereochemical configuration at C5 (i.e., 5α vs. 5ß) and the extent and sites of oxygenation (hydroxylation or ketonization) of the bile acid derived steroid skeleton were evaluated by screening the compounds for olfactory activity using electro-olfactogram recording. 5ß-Petromyzonol sulfate (9a) elicited a considerable olfactory response at sub-nanomolar concentration. In addition, less oxygenated systems (i.e., 9b-9e) elicited olfactory responses, albeit with less potency. The sea lamprey sex pheromone mimic 9f (5ß-3-ketopetromyzonol sulfate) was also examined and found to produce a much lower olfactory response. Mixture studies conducted with 9a and PS (1) suggest that stimulation is occurring via similar modes of activation, demonstrating a relative lack of specificity for recognition of the allo-configuration (i.e., 5α) in sea lamprey olfaction. This attribute could facilitate design of pheromone analogs to control this invasive species.

Chemical synthesis of (22E)-3alpha,6alpha,7alpha,12alpha-Tetrahydroxy-5beta-chol-22-en-24-oic acid and its N-acylamidated conjugates with glycine or taurine: precursors of the [22,23-(3)H] labelled tracers.

(22E)-3alpha,6alpha,7alpha,12alpha-Tetrahydroxy-5beta-chol-22-en-24-oic acid and its N-acylamidated conjugates with glycine or taurine were synthesized from cholic acid. The key reactions employed are: 1) degradation of the side chain in intermediary C(24) 3alpha,6alpha,7alpha,12alpha-tetrahydroxylated bile acid to the corresponding C(22) 23,24-dinor-aldehyde, followed by Wittig reaction with methyl (triphenylphosphoranylidene)acetate and 2) N-acylamidation of the unconjugated tetrahydroxy-Delta(22)-5beta-cholenoic acid with glycine (or taurine) in the presence of diethylphosphorocyanide and triethylamine as coupling reagents.

Synthesis, aggregation behavior and cholesterol solubilization studies of 16-epi-pythocholic acid (3 alpha,12 alpha,16 beta-trihydroxy-5 beta-cholan-24-oic acid).

Synthesis, aggregation behavior and in vitro cholesterol solubilization studies of 16-epi-pythocholic acid (3 alpha,12 alpha,16 beta-trihydroxy-5 beta-cholan-24-oic acid, EPCA) are reported. The synthesis of this unnatural epimer of pythocholic acid (3 alpha,12 alpha,16 alpha-trihydroxy-5 beta-cholan-24-oic acid, PCA) involves a series of simple and selective chemical transformations with an overall yield of 21% starting from readily available cholic acid (CA). The critical micellar concentration (CMC) of 16-epi-pythocholate in aqueous media was determined using pyrene as a fluorescent probe. In vitro cholesterol solubilization ability was evaluated using anhydrous cholesterol and results were compared with those of other natural di- and trihydroxy bile acids. These studies showed that 16-epi-pythocholic acid (16 beta-hydroxy-deoxycholic acid) behaves similar to cholic acid (CA) and avicholic acid (3 alpha,7 alpha,16 alpha-trihydroxy-5 beta-cholan-24-oic acid, ACA) in its aggregation behavior and cholesterol dissolution properties.

Synthesis of new, UV-photoactive dansyl derivatives for flow cytometric studies on bile acid uptake.

Four new fluorescent derivatives of cholic acid have been synthesized; they incorporate a dansyl moiety at 3alpha-, 3beta-, 7alpha- or 7beta- positions. These cholic acid analogs are UV photoactive and also exhibit green fluorescence. In addition, they have been demonstrated to be suitable for studying the kinetics of bile acid transport by flow cytometry.

Preparation and structural, biochemical, and pharmaceutical characterizations of bile acid-modified long-acting exendin-4 derivatives.

To develop an effective long-acting antidiabetic, the GLP-1 analogue of exendin-4 was modified with three different bile acids (BAs; cholic, deoxycholic, or lithocholic acid), at its two lysine residues. The biological, pharmaceutical, and physicochemical characteristics of these exendin-4 analogues were carefully investigated. Biological activity tests demonstrated that the monobile acid substitutions of exendin-4 showed well preserved receptor binding efficacy without noticeable insulinotropic or antidiabetic activity loss. However, physicochemical and pharmacokinetic studies revealed that the albumin-binding properties and in vivo elimination half-lives of BAM1-Ex4s (Lys(27)-BA-Ex4s) were significantly enhanced by increasing the hydrophobicities of the conjugated BAs. Furthermore, the protracted antidiabetic effects of the BAM1-Ex4s were also verified by the prolonged restoration of normoglycemia in type 2 diabetic mice. Accordingly, the present study suggests that the derivatization of exendin-4 with BAs offers a means of producing long-acting GLP-1 receptor agonists for type 2 diabetic therapy.

Addictive evaluation of cholic acid-verticinone ester, a potential cough therapeutic agent with agonist action of opioid receptor.

AIM: The purpose of this work was to search for potential drugs with potent antitussive and expectorant activities as well as a low toxicity, but without addictive properties. Cholic acid-verticinone ester (CA-Ver) was synthesized based on the clearly elucidated antitussive and expectorant activities of verticinone in bulbs of Fritillaria and different bile acids in Snake Bile. In our previous study, CA-Ver showed a much more potent activity than codeine phosphate. This study was carried out to investigate the central antitussive mechanism and the addictive evaluation of CA-Ver. METHODS: Testing on a capsaicin-induced cough model of mice pretreated with naloxone, a non-selective opioid receptor antagonist, was performed for the observation of CA-Ver's central antitussive mechanism. We then took naloxone-induced withdrawal tests of mice for the judgment of CA-Ver's addiction. Lastly, we determined the opioid dependence of CA-Ver in the guinea pig ileum. RESULTS: The test on the capsaicin-induced cough model showed that naloxone could block the antitussive effect of CA-Ver, suggesting the antitussive mechanism of CA-Ver was related to the central opioid receptors. The naloxone-urged withdrawal tests of the mice showed that CA-Ver was not addictive, and the test of the opioid dependence in the guinea pig ileum showed that CA-Ver had no withdrawal response. CONCLUSION: These findings suggested that CA-Ver deserved attention for its potent antitussive effects related to the central opioid receptors, but without addiction, and had a good development perspective.

Isolation and chemical synthesis of a major, novel biliary bile acid in the common wombat (Vombatus ursinus): 15alpha-hydroxylithocholic acid.

The major bile acids present in the gallbladder bile of the common Australian wombat (Vombatus ursinus) were isolated by preparative HPLC and identified by NMR as the taurine N-acylamidates of chenodeoxycholic acid (CDCA) and 15alpha-hydroxylithocholic acid (3alpha,15alpha-dihydroxy-5beta-cholan-24-oic acid). Taurine-conjugated CDCA constituted 78% of biliary bile acids, and (taurine-conjugated) 15alpha-hydroxylithocholic acid constituted 11%. Proof of structure of the latter compound was obtained by its synthesis from CDCA via a Delta14 intermediate. The synthesis of its C-15 epimer, 15beta-hydroxylithocholic acid (3alpha,15beta-dihydroxy-5beta-cholan-24-oic acid), is also reported. The taurine conjugate of 15alpha-hydroxylithocholic acid was synthesized and shown to have chromatographic and spectroscopic properties identical to those of the compound isolated from bile. It is likely that 15alpha-hydroxylithocholic acid is synthesized in the wombat hepatocyte by 15alpha-hydroxylation of lithocholic acid that was formed by bacterial 7alpha-dehydroxylation of CDCA in the distal intestine. Thus, the wombat appears to use 15alpha-hydroxylation as a novel detoxification mechanism for lithocholic acid.

Poly(choloyl)-based amphiphiles as pore-forming agents: transport-active monomers by design.

This paper describes the design and synthesis of a family of pore-forming amphiphiles. Two of these amphiphiles, which are derived from cholic acid, lysine, and p-phenylenediamine, can produce pores in lipid bilayers as individual molecules. In sharp contrast, analogous amphiphiles that do not contain a rigid 1,4-phenylenediamide moiety favor the formation of dimer-based pores. Kinetic evidence in support of monomer- and dimer-based pores has been obtained from Na+ transport measurements across bilayers made from 1-palmitoyl-2-oleoyl-2-sn-glycero-3-phosphocholine (POPC). Structure-activity studies that have been carried out with pore-forming, dimer-based amphiphiles have also revealed a significant activity dependence on their overall compactness. The practical potential of pore-forming amphiphiles with controllable supramolecular properties is briefly discussed.