In Vitro selectivity of an acyclic cucurbit[n]uril molecular container towards neuromuscular blocking agents relative to commonly used drugs

Anthracene Walled Acyclic CB[n] Receptors: In Vitro and In Vivo Binding Properties Toward Drugs of Abuse

We report studies of the interaction of six acyclic CB[n]-type receptors toward a panel of drugs of abuse by a combination of isothermal titration calorimetry and 1H NMR spectroscopy.  Anthracene walled acyclic CB[n] host (M3) displays highest binding affinity toward methamphetamine (Kd = 15 nM) and fentanyl (Kd = 4 nM).  Host M3 is well tolerated by Hep G2 and HEK 293 cells up to 100 mM according to MTS metabolic and adenylate kinase release assays.  An in vivomaximum tolerated dose study with Swiss Webster mice showed no adverse effects at the highest dose studied (44.7 mg kg-1). Host M3 is not mutagenic based on the Ames fluctuation test and does not inhibit the hERG ion channel.  In vivoefficacy studies showed that pretreatment of mice with M3 significantly reduces the hyperlocomotion after treatment with methamphetamine, but M3 does not function similarly when administered 30 seconds after methamphetamine.

Recent advances in supramolecular antidotes

Poisons always have fascinated humankind. Initially considered as deleterious or hazardous substances, the modern era has witnessed the controlled utilization of dangerous poisons in medicine and cosmetics. Simultaneously, antidotes have become crucial as reversal agents to counteract the effects of a poison, and they are also used today to positively cancel the benefits of a poison after use. Currently, the majority of poisons are composed of small molecules. This review focuses on recent developments to reverse or prevent toxic effects of poisons by encapsulation in host molecules. Cyclodextrins, cucurbiturils, acyclic cucurbituril derivatives, calixarenes, and pillararenes, have been reported to largely impact the effects of toxic compounds, thus extending the current paradigm of small molecule antidotes by adding a new family of macrocyclic compounds to the current arsenal of antidotes. Along this line of research, endogenous "harmful" species are also sequestered by one or more of these supramolecular host molecules, expanding the potential of supramolecular antidotes to diverse therapeutic areas.

Acyclic Cucurbit[n]uril-Type Containers as Receptors for Neuromuscular Blocking Agents: Structure-Binding Affinity Relationships

Acyclic cucurbit[n]uril molecular containers 1 and 2C3 have previously been shown to strongly bind to the neuromuscular blocking agents rocuronium, vecuronium, pancuronium, and cisatracurium in vitro by optical methods and to reverse neuromuscular block in vivo in rats. In this paper we study the in vitro binding of a panel of acyclic CB[n]-type receptors toward the four neuromuscular blocking agents and acetylcholine to develop structure-binding affinity relationships. The selected variants include those with different aromatic sidewalls (e.g. 1Me₄ with dimethyl o-xylylene walls; 3 with 1,8-linked naphthalene walls), with different glycoluril oligomer lengths (e.g. 4 and 5 based on glycoluril trimer), and with different linker lengths between aromatic wall and SO₃ ^- solubilizing group (e.g. 2C2 - 2C4). Based on the analysis of complexation induced changes in ¹H NMR chemical shift we conclude that the hydrophobic regions of the guests bind in the hydrophobic cavity of the hosts with the cationic moieties of the guest binding at the ureidyl C=O portals by ion-dipole and ion-ion interactions. The thermodynamic parameters of binding were determined by direct and competition isothermal titration calorimetry experiments. We find that hosts 4 and 5 based on glycoluril trimer form significantly weaker complexes with the streroidal NMBAs than with the analogues hosts based on glycoluril tetramer (1 and 2C3). Similarly, hosts 1Me₄ and 3 with different length and height aromatic walls do not exhibit the extreme binding constants displayed by 2C3 but rather behave similarly to 1. Finally, we find that hosts 2C2 and 2C4 bind only slightly more weakly to the NMBAs than 2C3, but retain the ability to discriminate against acetylcholine, and possess higher inherent water solubility than 2C3. Host 2C4, in particular, holds potential for future in vivo applications.

Gas-phase study of the stability of α-substituted cyclic amino nitriles under electron ionization and electrospray ionization and fragmentation peculiarities of cyclic ketimines

RATIONALE

α-Substituted cyclic amino nitriles show different reactivity and stability in solution depending on their ring size. Mass-spectrometric modeling of the reactions, which normally take place in solution, may shed light on the nature of the studied compounds and explain some observations.

METHODS

The stability of the nitriles in an acidic solution was studied by adding glacial acetic acid. Gas-phase modelling was conducted by gas chromatography/mass spectrometry (GC/MS) with electron ionization mass spectrometry and direct inlet electrospray ionization. QqQ and Orbitrap analyzers were used to carry out tandem mass spectrometry (MS/MS) experiments.

RESULTS

The obtained data show that the elimination of HCN from α-substituted cyclic amino nitriles occurs in the same way for an acidic solution, thermolysis and electrospray ionization. According to GC, the most stable were N-formylated nitriles compared with N-benzylated or N-unsubstituted ones. Electrospray ionization demonstrated its advantages for the routine identification of cyclic amino nitriles due to milder conditions than in electron ionization. Fragmentations of cyclic ketimines, formed from N-unsubstituted amino nitriles, are discussed in particular.

CONCLUSIONS

Similarities in the behavior of the α-substituted cyclic amino nitriles under electron ionization, electrospray ionization, thermolysis and reaction in solution under acidic catalysis were discovered and confirmed by MS/MS experiments. Fragmentation schemes of the studied nitriles and corresponding imines are proposed.

Acyclic Cucurbit[n]uril-Type Receptors: Optimization of Electrostatic Interactions for Dicationic Guests

The synthesis of acyclic CB[n]-type host (1) is reported. By optimizing the placement of the sulfate groups nearby the electrostatically negative ureidyl C═O portals, the binding affinity of this class of receptors toward hydrophobic (di)ammonium guest molecules (5-23) is maximized. The X-ray crystal structures of 1·6a and 1·6d are reported.

Calabadion 1 selectively reverses respiratory and central nervous system effects of fentanyl in a rat model

BACKGROUND

We hypothesised that Calabadion 1, an acyclic cucurbit[n]uril molecular container, reverses fentanyl-induced respiratory depression and dysfunction of the CNS.

METHODS

Experiments were conducted in male Sprague-Dawley rats. A constant-rate i.v. infusion of fentanyl (12.5 or 25 μg kg^-1 over 15 min) was administered followed by an i.v. bolus of Calabadion 1 (0.5-200 mg kg^-1) or placebo. The primary outcome was reversal of ventilatory and respiratory depression, assessed by pneumotachography and arterial blood gas analysis, respectively. Key secondary outcomes were effects on fentanyl-induced central nervous dysfunction quantified by righting reflex, balance beam test, and electromyography (EMG).

RESULTS

Calabadion 1 reversed fentanyl-induced respiratory depression across the endpoints minute ventilation, pH, and Paco₂ (P=0.001). Compared with placebo, Calabadion 1 dose dependently (P for trend <0.001) reversed fentanyl-induced hypoventilation {81.9 [5.1] (mean [standard error of the mean]) vs 45.5 [12.4] ml min^-1; P<0.001}, acidosis (pH 7.43 [0.01] vs 7.28 [0.04]; P=0.005), and hypercarbia (Paco₂ 43.4 [1.6] vs 63.4 [8.1] mm Hg; P=0.018). The effective Calabadion 1 doses required to reverse respiratory depression by 50% and 90% (ED50_Res and ED90_Res) were 1.7 and 15.6 mg kg^-1, respectively. Higher effective doses were needed for recovery of righting reflex (ED50_CNS: 9.6 mg kg^-1; ED90_CNS: 86.1 mg kg^-1), which was accelerated by Calabadion 1 (4.6 [0.3] vs 9.0 [0.7] min; P<0.001). Calabadion 1 also significantly accelerated recovery of full functional mobility and reversal of muscle rigidity.

CONCLUSIONS

Calabadion 1 selectively and dose dependently reversed the respiratory system and CNS side-effects of fentanyl.

Triazole functionalized acyclic cucurbit[n]uril-type receptors: host·guest recognition properties

We report the synthesis of three new triazole functionalized acyclic CB[n]-type receptors (2-4) by click chemistry. The compounds have good solubility in water (≥8 mM) and do not undergo strong self-association (Ks ≤ 903 M-1). We measured the binding constants of 2-4 toward guests 9-24 and compared the results to those obtained for the prototypical acyclic CB[n]-type receptor 1. The X-ray crystal structure of 4 is also described.

Functionalisable acyclic cucurbiturils

Functionalised acyclic cucurbiturils can be prepared in a straightforward fashion and provide access to a wide variety of substituted derivatives.

Acyclic Cucurbit[n]uril-type Receptors: Preparation, Molecular Recognition Properties and Biological Applications

This article traces the development of acyclic cucurbit[n]uril-type receptors with a focus on work from the Isaacs group. First, we describe the synthesis of methylene bridged glycoluril dimers capped with aromatic sidewalls which allowed us to probe the interconversion of the S- and C-shaped dimers which is a fundamental step in CB[n] formation. The C-shaped compounds were found to undergo discrete self-assembly (dimerization) in both water and organic solvents which lead us to investigate multicomponent self-sorting systems. We supressed the self-association of 8 by electrostatic repulsion in the putative dimer which allowed expression of its innate molecular recognition properties toward methylene blue and related planar cationic dyes. Longer glycoluril oligomers (trimer - hexamer, acyclic decamer) were prepared by starving the CB[n]-forming reaction of formaldehyde. The longer oligomers (e.g. 15 and 16) bind to alkylammonium ions in water ≈ 100-fold weaker than macrocyclic CB[n] highlighting the high preorganization of the acyclic but polycyclic framework. We prepared a wide variety of acyclic CB[n] compounds (wall variants, solubilizing group variants, linker variants) based on glycoluril trimer and tetramer. In particular, 26 and 27 have been shown to possess a wide variety of chemically and biologically interesting functions. For example, 26 was used to formulate the insoluble drug Albendazole and treat mice bearing SK-OV-3 xenograft tumors. Compound 27 binds tightly to the neuromuscular blocking agents rocuronium, vecuronium, and cisatracurium and acts as an in vivo reversal agent for these compounds in anesthetized rats. Container 27 was also found to modulate the hyperlocomotive effect of rats that had been treated with methamphetamine. Finally, 38 has been used as a cross reactive component of sensor arrays that are capable of classifying and quantifying cancer related nitroamines and a range of over the counter drugs. Overall, the work demonstrates that acyclic CB[n]-type compounds are nicely pre-organized and therefore retain the essential aspects of the recognition properties of macrocyclic CB[n] but allow for more straightforward tailoring of structure and solubility that enables a variety of chemically and biologically important applications.

Enantioselective synthesis of α-perfluoroalkylated prolines, their 6,7-membered homologues and derivatives

The highly enantioselective Strecker reaction with alpha-perfluoroalkylated cyclic ketimines was reported. The corresponding asymmetric cyclic nitriles are a useful tool for obtaining amino acids and their derivatives.

Molecular Containers Bind Drugs of Abuse in Vitro and Reverse the Hyperlocomotive Effect of Methamphetamine in Rats

We measured the affinity of five molecular container compounds (calabadions 1 and 2, CB[7], sulfocalix[4]arene, and HP-β-CD) toward seven drugs of abuse in homogenous aqueous solution at physiological pH by various methods (1 H NMR, UV/Vis, isothermal titration calorimetry [ITC]) and found binding constants (Ka values) spanning from <102 to >108  m-1 . We also report X-ray crystal structures of CB[7]⋅methamphetamine and 1⋅methamphetamine. We found that 2, but not CB[7], was able to ameliorate the hyperlocomotive activity of rats treated with methamphetamine. The bioavailability of the calabadions and their convergent building block synthesis suggest potential for further structural optimization as reversal agents for intoxication with nonopioid drugs of abuse for which no treatments are currently available.

Drug delivery by supramolecular design

Principles rooted in supramolecular chemistry have empowered new and highly functional therapeutics and drug delivery devices. This general approach offers elegant tools rooted in molecular and materials engineered to address the many challenges faced in treating disease.