Bile acid amidoalcohols: simple organogelators

Hybrid hydrogels derived from renewable resources as a smart stimuli responsive soft material for drug delivery applications

The design and synthesis of amphiphilic molecules play a crucial role in fabricating smart functional materials via self-assembly. Especially, biologically significant natural molecules and their structural analogues have inspired chemists and made a major contribution to the development of advanced smart materials. In this report, a series of amphiphilic N-acyl amides were synthesized from natural precursors using a simple synthetic protocol. Interestingly, the self-assembly of amphiphiles 6a and 7a furnished a hydrogel and oleogel in vegetable oils. Morphological analysis of gels revealed the existence of a 3-dimensional fibrous network. Thermoresponsive and thixotropic behavior of these gels were evaluated using rheological analysis. A composite gel prepared by the encapsulation of curcumin in the hydrogel formed from 7a displayed a gel-sol transition in response to pH and could act as a dual channel responsive drug carrier.

Design, synthesis, spectral and theoretical study of new bile acid-sterol conjugates linked via 1,2,3-triazole ring

New four steroid conjugates have been prepared from bile acids and sterol derivatives using click chemistry method. The azide-alkyne Huisgen cycloaddition (intermolecular 1,3-dipolar cycloaddition) of the propargyl ester of lithocholic, deoxycholic, cholic acid as well as dehydrocholic acids and azide derivatives of cholesterol gave a new bile acid-sterol conjugates linked with a 1,2,3-triazole ring. Previously, bile acids were converted into bromoacetyl substituted derivatives by the reaction of propargyl esters of lithocholic, deoxycholic, cholic with bromoacetic acid bromide in toluene with TEBA and sodium hydride. All conjugates were obtained in good yields using an efficient synthesis method. The structures of all products were confirmed by spectral (¹H- and ¹³C NMR, and FT-IR) analysis, mass spectrometry (ESI-MS), as well as PM5 semiempirical methods. Estimation of the pharmacotherapeutic potential has been accomplished for the synthesized compounds on the basis of Prediction of Activity Spectra for Substances (PASS).

Recent advances in the bile acid based conjugates/derivatives towards their gelation applications

Bile acids have contributed immensely to hydrogel research due to their peculiar physicochemical properties and biocompatibility. The wide accessibility of bile acids and their straightforward derivatization methods make them attractive building blocks for the design of novel hydrogels systems to deliver biomolecules, drugs, and vaccines. This review conceptualizes recent developments in bile acid-based hydrogels and their applications. These bile-based hydrogels have the ability to absorb carbon dioxide efficiently and may potentially work as alternative materials for carbon dioxide capture and storage. The hydrogels hold great potential in medicine and biology applications as drug carriers and models for fundamental self-assembly in pathological conditions. Herein, we have summarized the efforts that have been made for the development of molecular hydrogels in terms of biocompatibility, therapeutic applications, and challenges associated with existing molecular hydrogels.

Novel Derivatives of Deoxycholic Acid Bearing Linear Aliphatic Diamine and Aminoalcohol Moieties and their Cyclic Analogs at the C3 Position: Synthesis and Evaluation of Their In Vitro Antitumor Potential

A series of novel deoxycholic acid (DCA) derivatives containing aliphatic diamine and aminoalcohol or morpholine moieties at the C3 position were synthesized by 3,26-epoxide ring-opening reactions. These compounds were investigated for their cytotoxicity in four human tumor cell lines and murine macrophages and for inhibitory activity against macrophage-mediated NO synthesis in vitro. Obtained data revealed that: (i) all amine-containing substituents significantly increased the cytotoxicity of the novel compounds (IC₅₀^2–10 = 1.0–36.0 μM) in comparison with DCA (IC₅₀^DCA ≥ 82.9 μM); (ii) aminoalcohol moieties were more preferable than diamine moieties due to the fact they imparted better selectivity for tumor cells of the novel derivatives; (iii) the susceptibility of tested cell lines to derivatives diminished in the following order: HuTu-80 (duodenal carcinoma) ≈ HepG2 (hepatocarcinoma) > KB-3-1 (cervical carcinoma) > RAW264.7 (macrophages) > A549 (lung carcinoma); (iv) compounds 8 and 9, bearing aminoethanol and aminopropanol moieties, respectively, exhibited high cytotoxic selectivity indexes (SI^HuTu-80 = 7.9 and 8.3, respectively) and good drug-likeness parameters; (v) the novel compounds do not display anti-NO activity. Mechanistic study revealed that compound 9 induces ROS-dependent cell death by activation of intrinsic caspase-dependent apoptosis and cytodestructive autophagy in HuTu-80 cells and vitamin D receptor can be considered as its primary target.

Design and gelation behaviors of cholesterol-based derivatives as organogelators: an investigation of the correlation between molecular structures and gelation behaviors

The carboxylic group and the number of cholesteryl moieties have an important influence on gelation behaviors.

Biocompatible hydrogelators based on bile acid ethyl amides

Four novel bile acid ethyl amides were synthetized using a well-known method. All the four compounds were characterized by IR, SEM, and X-ray crystal analyses. In addition, the cytotoxicity of the compounds was tested. Two of the prepared compounds formed organogels. Lithocholic acid derivative 1 formed hydrogels as 1% and 2% (w/v) in four different aqueous solutions. This is very intriguing regarding possible uses in biomedicine.

Bile acid hydrazides: gelation, structural, physical and spectroscopic properties

Novel bile acid hydrazides are synthesized and temperature dependent NMR, IR and rheological experiments are done for understanding the role of intra-molecular hydrogen bonding leading to gelation.

Synthesis, spectroscopic and theoretical studies of new quasi-podands from bile acid derivatives linked by 1,2,3-triazole rings

A novel method for the synthesis of bile acid derivatives has been developed using "click chemistry". Intermolecular 1,3-dipolar cycloaddition of the propargyl ester of bile acids and azide groups of 1,3,5-tris(azidomethyl)benzene gave a new quasi-podands with 1,2,3-triazole rings. The structures of the products were confirmed by spectral (1H-NMR, 13C-NMR, and FT-IR) analysis, mass spectrometry and PM5 semiempirical methods. Estimation of the pharmacotherapeutic potential has been accomplished for synthesized compounds on the basis of Prediction of Activity Spectra for Substances (PASS).

New polyfluorothiopropanoyloxy derivatives of 5β-cholan-24-oic acid designed as drug absorption modifiers

A series of final six propanoyloxy derivatives of 5β-cholan-24-oic acid (tridecafluoroctylsulfanyl- and tridecafluoroctylsulfinylethoxycarbonylpropanoyloxy derivatives) as potential drug absorption promoters (skin penetration enhancers, intestinal absorption promoters) was generated by multistep synthesis. Structure confirmation of all generated compounds was accomplished by (1)H NMR, (13)C NMR, IR and MS spectroscopy methods. All the prepared compounds were analyzed using RP-TLC, and their lipophilicity (RM) was determined. The hydrophobicity (log P), solubility (logS), polar surface area (PSA) and molar volume (MV) of the studied compounds were also calculated. All the target compounds were tested for their in vitro transdermal penetration effect and as potential intestinal absorption enhancers. The cytotoxicity of all the evaluated compounds was evaluated against normal human skin fibroblast cells. Their anti-proliferative activity was also assessed against human cancer cell lines: T-lymphoblastic leukaemia cell line and breast adenocarcinoma cell line. One compound showed high selective cytotoxicity against human skin fibroblast cells and another compound possessed high cytotoxicity against breast adenocarcinoma cell line and skin fibroblast cells. Only one compound expressed anti-proliferative effect on leukaemia and breast adenocarcinoma cells without affecting the growth of normal cells, which should be promising in potential development of new drugs. Most of the target compounds showed minimal anti-proliferative activity (IC50>37μM), indicating they would have moderate cytotoxicity when administered as chemical absorption modifiers. The relationships between the lipophilicity/polarity and the chemical structure of the studied compounds as well as the relationships between their chemical structure and penetration enhancement effect are discussed in this article.

New propanoyloxy derivatives of 5β-cholan-24-oic acid as drug absorption modifiers

A series of final twelve propanoyloxy derivatives of 5β-cholan-24-oic acid (O-propanoyl derivatives of cholic acid) as potential drug absorption modifiers (skin penetration enhancers, intestinal absorption promoters) was generated by multistep synthesis. Structure confirmation of all generated compounds was accomplished by 1H NMR, 13C NMR, IR and MS spectroscopy methods. All the prepared compounds were analyzed using RP-TLC, and their lipophilicity (RM) was determined. The hydrophobicity (log P), solubility (log S), polar surface area (PSA) and molar volume (MV) of the studied compounds were also calculated. All the target compounds were tested for their in vitro transdermal penetration effect and as potential intestinal absorption enhancers. The cytotoxicity of all the evaluated compounds was evaluated against normal human skin fibroblast cells. Their anti-proliferative activity was also assessed against human cancer cell lines: T-lymphoblastic leukemia cell line and breast adenocarcinoma cell line. One compound showed selective cytotoxicity against human skin fibroblast cells and another compound possessed the highest cytotoxicity against all the tested cell lines. Only one compound expressed anti-proliferative effect on leukemia cancer cells without affecting the growth of normal cells, which should be promising in potential development of new drugs. Most of the target compounds showed minimal anti-proliferative activity (IC50>37 μM), indicating they would have moderate cytotoxicity when administered as chemical absorption modifiers. The relationships between the lipophilicity/polarity and the chemical structure of the studied compounds as well as the relationships between their chemical structure and enhancement effect are discussed in this article.

Bile acid-cysteamine conjugates: structural properties, gelation, and toxicity evaluation

Design, synthesis, and characterization of six novel bile acid-cysteamine conjugates together with investigation of their structural studies, gelation properties, and preliminary toxicity evaluation, are reported. Solid state properties of selected compounds were studied by means of X-ray diffraction and (13)C CPMAS NMR spectroscopy. N-(2-thioethyl)-3α,7α,12α-trihydroxy-5β-cholan-24-amide was shown to exhibit (pseudo)polymorphism, and a single crystal structure of its non-stoichiometric hydrate is reported herein. Cholyl and dehydrocholyl derivatives bearing three functionalities in their steroidal backbone were shown to undergo self-assembly leading to gelation in certain organic solvents. Preliminary morphology studies of the formed gels by scanning electron microscopy (SEM) were performed. The standard model mouse fibroblast cell line together with the MTT and NR tests were utilized for evaluating the toxicity of the prepared compounds. Lithocholyl, ursodeoxycholyl, and dehydrocholyl derivatives turned out to be relatively non-toxic in the conditions studied.

Investigation of new acyloxy derivatives of cholic acid and their esters as drug absorption modifiers

Skin penetration enhancers are used in the formulation of transdermal delivery systems for drugs that are otherwise not sufficiently skin-permeable. Intestinal absorption promoters/enhancers are used as excipients in oral formulations of poorly oral-bioavailable drugs. Series of fourteen acyloxy derivatives of 5β-cholic acid as potential drug absorption modifiers was generated by multistep synthesis. The synthesis of all newly prepared compounds is presented here. Structure confirmation of all generated compounds was accomplished by (1)H NMR, (13)C NMR, IR and MS spectroscopy methods. All the prepared compounds were analyzed using RP-TLC, and their lipophilicity (R(M)) was determined. The hydrophobicity (logP) and solubility (logS) of the studied compounds were also calculated using two commercially available programs. All the target compounds were tested for their in vitro transdermal penetration activity and as potential intestinal absorption enhancers. The anti-proliferative activity of all the final compounds was also assessed against the human cancer cell lines: T-lymphoblastic leukemia cell line and the breast adenocarcinoma cell line. Their cytotoxicity was also evaluated against the normal human skin fibroblast cells. Two compounds showed anti-proliferative effect on cancer cells without affecting the growth of normal cells, which should be promising in potential development of new drugs. Most of the target compounds showed minimal anti-proliferative activity (IC(50)>37 μM), indicating they would have low cytotoxicity when administered as chemical absorption modifiers. The relationships between the lipophilicity and the chemical structure of the studied compounds as well as the relationships between their chemical structure and enhancement effects are discussed in this article.

Synthesis of both ionic species of ammonium dithiocarbamate derived cholic acid moieties

The reaction of 3-aminopropylamide of cholic acid with CS₂ produced a bile acid derivative of dithiocarbamic acid which further formed an ammonium salt with another molecule of 3-aminopropylamide of cholic acid. The cationic 3-ammonium propylamide of cholic acid did not react further with CS₂ and the formed salt was stable in the reaction mixture, even when excess CS₂ was used. When the reaction was carried out in the presence of aqueous sodium hydroxide, only the bile acid derivative of sodium dithiocarbamate was formed. The dithiocarbamate derivatives were characterized by ¹H- and ¹³C-NMR spectroscopy and ESI-TOF mass spectrometry.

Thermosensitivity of bile acid-based oligo(ethylene glycol) stars in aqueous solutions

Amphiphilic star-shaped oligo(ethylene glycol)s with a hydrophobic bile acid core and varying number of hydrophilic arms have been made. Their thermal behavior in aqueous solutions depends on the number rather than the length of the arms. The two-armed lithocholate derivative showed the strongest tendency for association and exhibited the lowest cloud point (79 °C) of the oligomers made, as well as another phase separation at a lower temperature (31 °C). The "double thermosensitivity" arising both from the salt-dependent LCST of the oligo(ethylene glycol) segments and the temperature-responsive self-assembly of amphiphilic bile acid derivative provides an interesting path in the design of bile acid-based smart materials.

Microwave assisted synthesis and solid-state characterization of lithocholyl amides of isomeric aminopyridines

Microwave (MW) assisted synthesis and solid state structural characterizations of novel lithocholyl amides of 2-, 3-, and 4-aminopyridine are reported. It is shown that the MW technique is a proper method in the preparation of N-lithocholyl amides of isomeric aminopyridines. It offers many advantages compared to conventional heating. The molecular and crystal structures as well as the polymorphic and hydrated forms of prepared conjugates with their thermodynamic stabilities have been characterized by means of high resolution liquid- and solid-state NMR spectroscopy, single crystal and powder X-ray diffraction, and thermogravimetric analysis. Owing to the many biological functions of bile acids and amino substituted nitrogen heterocycles, knowledge of the crystal packing of these novel conjugates may have relevance for potential pharmaceutical applications.

Self-assembly of esters of arjunolic acid into fibrous networks and the properties of their organogels

Nine esters of a naturally occurring triterpenoid, arjunolic acid (from Terminalia arjuna), with alkyl chains have been synthesized, and their self-assembly has been studied in organic liquids. All of the esters examined were found to be excellent gelators. No birefringence was detected in optical micrographs of the transparent toluene gels with 5% (w/w) ethyl arjunolate or 5% (w/w) p-nitrobenzyl arjunolate as the gelator, but a spherulitic-type pattern was seen for a gel of 1.2% (w/w) p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane. Electron microscope images revealed self-assembled fibrillar network (SAFIN) structures with right-handed helical ribbons in some gels. With increasing concentration of the gelators, the gel-to-sol transition temperature (T(gel)) increased and then approached plateau values. Differential scanning thermograms demonstrated that the heats for transition from transparent gels to sols of ethyl arjunolate or p-nitrobenzyl ajunolate in toluene are very small. Powder X-ray diffractograms revealed that the molecular packing in the SAFIN of the 5% (w/w) ethyl aijunoate in the toluene gel was amorphous and similar to the diffractogram recorded for the neat gelator. Although the diffractogram of neat p-nitrobenzyl arjunolate consisted of broad peaks, suggesting disordered packing, the low-angle peaks of the corresponding toluene gel were much sharper; these results indicate more crystalline packing in the SAFIN than in the neat gelator. The kinetics and growth of the transformation of sols of p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane to their gels have been investigated at different incubation temperatures by circular dichroism spectroscopy. The data have been analyzed to probe the mechanism of SAFIN formation and the relationship between the molecular structures of the esters of arjunolic acid and their abilities to function as gelators of a wide variety of organic liquids.

3α-Hydr-oxy-N-(3-hydroxy-prop-yl)-5β-cholan-24-amide

The title compound, C(27)H(47)NO(3), is a (3-hydroxy-prop-yl)amide derivative of naturally occurring enanti-opure lithocholic acid (3α-hydr-oxy-5β-cholan-24-oic acid). The mol-ecule contains four fused rings: three six-membered rings in chair conformations and one five-membered ring in a half-chair form. The two terminal six-membered rings are cis-fused, while other rings are trans-fused. The structure contains an intra-molecular O-H⋯O hydrogen bond and a similar hydrogen-bond framework to the corresponding deoxy-cholic and chenodeoxy-cholic acid derivatives. Inter-molecular O-H⋯O and N-H⋯O inter-actions are also present in the crystal. This compound seems to have at least two polymorphic forms from a comparison of the X-ray powder pattern simulated from the present structure of the title compound and that previously obtained for the powder sample.

Syntheses and structural study of bile acid amidoalcohols

Preparation, structural and thermoanalytical characterization of fourteen N-hydroxyalkyl 5beta-cholan-24-amides have been performed in this study. The utilized techniques include liquid state and CP-MAS 13C NMR spectroscopy, thermogravimetry, differential scanning calorimetry, and also powder and single crystal X-ray crystallography. The results were discussed and compared to each other and also to previous findings on similar compounds. One pure hydrate form was obtained. Six new single crystal structures were determined, including one hydrated chloroform solvate. Decomposition temperatures were found to correlate with the side chain length, and the number of the hydroxyl groups. The spatial direction of the groups in the steroid skeleton was also found to be relevant in predicting the thermal properties of bile acid amidoalcohols studied.

Synthesis of Novel Amide-Linked Dimers of Lithocholic Acid

An efficient synthesis of lithocholic amides and amide-linked dimers under mild conditions is described. New o-, m- and p-phenylenediamine-derived dimers of lithocholic acid were synthesised by the activation of the carboxyl group of the bile acid as a mixed anhydride resulting from the reaction of the acid with ethyl chloroformate. The reduction of lithocholic amides afforded the corresponding 24-amino-5β-cholane derivatives. All compounds were characterised by IR, 1H and 13C NMR and mass spectra.

Simple esters of cholic acid as potent organogelators: direct imaging of the collapse of SAFINs

Unusual gelation of a number of organic solvents by allyl cholate and other simple esters of cholic acid is reported. These gels were characterized by SEM, AFM, polarizing optical microscopy (POM), X-ray powder diffraction and other techniques. Electron micrographs of the xerogels revealed the presence of highly entangled 3D fibrillar networks. Direct imaging of the collapse of SAFINs and their thermal stability were performed using variable temperature polarizing optical microscopy (POM).

Structural, thermoanalytical and molecular modeling studies on N-(3-hydroxypropyl) 3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-amide and its monohydrates

The synthetic method for preparing N-(3-hydroxypropyl) 3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-amide can lead to formation of at least three different crystal forms - an anhydrous compound and two monohydrates. The structural and thermal properties of these forms have been characterized by 13C-CP/MAS-NMR and IR spectroscopy, thermo- gravimetry, differential scanning calorimetry and by powder and single crystal x-ray crystallography. In addition, theoretical 13C-NMR chemical shift calculations were also performed for the anhydrous compound and for the first monohydrate, starting from single crystal structures and the structures of these species have now been verified. The first monohydrate, C27H47NO4 x H2O, crystallizes in orthorhombic space group P2(1)2(1)2(1) with cell parameters: a = 7.1148(2), b = 18.1775(5), c = 20.1813(6), Z = 4.

Molecular organogels. Soft matter comprised of low-molecular-mass organic gelators and organic liquids

This Account presents recent advances in understanding how and why dilute solutions/sols of low-molecular-mass organic gelators (LMOGs) undergo microscopic phase separation to form self-assembled fibrillar networks in molecular organogels. Concepts are illustrated structurally at the subnanometer (molecular) to several millimeter (bulk) length scales and dynamically over time scales that follow the assembly of supersaturated solutions/sols into gel phases. Examples include both structurally complicated (ALSmolecules with aromatic, linking, and steroidal groups) and simple (n-alkanes or n-alkanes along whose chains a hetero-group has been inserted) LMOGs in a wide range of organic liquids.

Organogels Derived from Tetranitrated Crown Ethers

[reaction: see text] The 3,3',4'4'-tetranitrodibenzocrown ethers TNDB24C8 and TNDB30C10 form organogels with chloroalkanes at 3% w/v. Atomic force microscopy and scanning electron microscopy have been used to characterize the superstructure of the gels. Gels prepared using TNDB30C10 and CHCl(3) are more fibrous and are ordered into elongated domains attributable to exposed parts of intermingled fibers. Differential scanning calorimetry shows that the gel aids in the formation of supercooled CHCl(3) (DeltaT = 21 K, DeltaH(av) = 19.0 +/- 1.5 kJ mol(-)(1)) and that the gel liquefies at 307 K.

Gelation of fluorinated liquids by non-fluorinated low-molecular-mass molecules

A family of tetrahydroxy diesters has been synthesised and observed to gel a range of fluorinated solvents and their mixtures; the phase behaviour and gel microstructure are reported for a homologous family of these diesters in blends of 1H,1H-heptafluorobutanol (HFB) and 2H,3H-perfluoropentane (HPFP).