ACD Labs Research Articles

HSQC Spectra Simulation and Matching for Molecular Identification.

In the pursuit of improved compound identification and database search tasks, this study explores heteronuclear single quantum coherence (HSQC) spectra simulation and matching methodologies. HSQC spectra serve as unique molecular fingerprints, enabling a valuable balance of data collection time and information richness. We conducted a comprehensive evaluation of the following four HSQC simulation techniques: ACD/Labs (ACD), MestReNova (MNova), Gaussian NMR calculations (DFT), and a graph-based neural network (ML). For the latter two techniques, we developed a reconstruction logic to combine proton and carbon 1D spectra into HSQC spectra. The methodology involved the implementation of three peak-matching strategies (minimum-sum, Euclidean-distance, and Hungarian distance) combined with three padding strategies (zero-padding, peak-truncated, and nearest-neighbor double assignment). We found that coupling these strategies with a robust simulation technique facilitates the accurate identification of correct molecules from similar analogues (regio- and stereoisomers) and allows for fast and accurate large database searches. Furthermore, we demonstrated the efficacy of the best-performing methodology by rectifying the structures of a set of previously misidentified molecules. This research indicates that effective HSQC spectral simulation and matching methodologies significantly facilitate molecular structure elucidation. Furthermore, we offer a Google Colab notebook for researchers to use our methods on their own data (https://github.com/AstraZeneca/hsqc_structure_elucidation.git).

In silico prediction of some pharmacokinetic, safety, biological activity and molecular docking studies of 1-piperazine indole hybrid with nicotinic amide and nicotinic acid and their analogues.

In silico predictions are now being utilized in drug discovery and design to assess the physicochemical, pharmacokinetics, and safety properties of compounds at the beginning of the drug discovery process. This early evaluation of the physicochemical, pharmacokinetics, and safety properties of compounds helps the researchers to invest their time and resources only in the best prospective lead compounds by eliminating compounds with a low chance of success. The purpose of this study was to explore a promising lead compound designed from 1-piperazine indole hybrid with nicotinic amide and nicotinic acid analogs targeted on Trypanosoma brucei phosphofructokinase for Trypanosomiasis activity by using in silico predictions strategy. The physicochemical, safety, pharmacokinetic, and biological activity properties of those molecules were predicted by using ADMETlab 2.0, ACD labs Chem Sketch software version 14.0, Molinspiration software, and MolPredictX online tool. Our results indicate that several promising candidates exhibit favorable characteristics. Based on Molinspiration software both nicotinic acid and nicotinic amide derivatives showed higher kinase inhibitor activity and all nicotinic acid derivatives revealed enzyme inhibitors and GPCR ligand activity. According to the MolPredictX online tool, the most biologically active derivatives were NA-4, NA-11, and NAD-11. Overall, our findings offer valuable insights into the potential efficacy and safety of these compounds. It appears that almost all of the compounds have successfully passed the pharmacokinetic evaluations and integration of nicotinic acid into indole appears to be more beneficial than nicotinic amide regarding certain biological activities.

Challenges with retention and recovery of impurities containing acidic moieties during analytical UHPLC method development and validation for gefapixant freebase

Gefapixant citrate is a P2X3 purinergic receptor antagonist developed for the treatment of chronic cough. Gefapixant freebase is the penultimate intermediate in the commercial manufacturing route for gefapixant citrate and contains a complex impurity profile consisting of acidic and basic analytes. A UHPLC method was developed for assay and purity determination of gefapixant freebase utilizing a Waters Acquity Charged Surface Hybrid (CSH) C18 column (2.1 mm I.D. x 10 cm length, 1.7 µm particle size) with 0.1 % phosphoric acid and acetonitrile as the mobile phases. Method optimization was performed using ACD Labs LC Simulator to achieve baseline separation of all impurities and the method was successfully validated. During routine use and method transfer for gefapixant freebase, an increase in retention time for impurities containing strongly acidic functional groups, and poor recovery of a sulfinic acid impurity were observed. Subsequent investigation determined that the CSH column aging resulting from exposure of the column packing to the acidic mobile phase was the root cause for these behaviors. The mechanism of peak-shifting was further investigated using model compounds and determined to be due to an increase in ionic interactions with the CSH stationary phase with routine column use. The increase in ionic interactions was demonstrated to correlate with the charge state of the analyte. Poor recovery for the sulfinic acid impurity was attributed to increased peak tailing for this single impurity on older columns. This knowledge was leveraged to establish additional system suitability requirements to monitor column performance for the lifecycle of the analytical procedure.

Novel Cyclopentaquinoline and Acridine Analogs as Multifunctional, Potent Drug Candidates in Alzheimer's Disease.

A series of new cyclopentaquinoline derivatives with 9-acridinecarboxylic acid and a different alkyl chain length were synthesized, and their ability to inhibit cholinesterases was evaluated. All designed compounds, except derivative 3f, exhibited a selectivity for butyrylcholinesterase (BuChE) with IC50 values ranging from 103 to 539 nM. The 3b derivative revealed the highest inhibitory activity towards BuChE (IC50 = 103.73 nM) and a suitable activity against AChE (IC50 = 272.33 nM). The 3f derivative was the most active compound to AChE (IC50 = 113.34 nM) with satisfactory activity towards BuChE (IC50 = 203.52 nM). The potential hepatotoxic effect was evaluated for both 3b and 3f compounds. The 3b and 3f potential antioxidant activity was measured using the ORAC-FL method. The 3b and 3f derivatives revealed a significantly higher antioxidant potency, respectively 35 and 25 higher than tacrine. Theoretical, physicochemical, and pharmacokinetic properties were calculated using ACD Labs Percepta software. Molecular modeling and kinetic study were used to reveal the mechanism of cholinesterase inhibition in the most potent compounds: 3b and 3f.

New Tetrahydroacridine Hybrids with Dichlorobenzoic Acid Moiety Demonstrating Multifunctional Potential for the Treatment of Alzheimer's Disease.

A series of new tetrahydroacridine and 3,5-dichlorobenzoic acid hybrids with different spacers were designed, synthesized, and evaluated for their ability to inhibit both cholinesterase enzymes. Compounds 3a, 3b, 3f, and 3g exhibited selective butyrylcholinesterase (EqBuChE) inhibition with IC50 values ranging from 24 to 607 nM. Among them, compound 3b was the most active (IC50 = 24 nM). Additionally, 3c (IC50 for EeAChE = 25 nM and IC50 for EqBuChE = 123 nM) displayed dual cholinesterase inhibitory activity and was the most active compound against acetylcholinesterase (AChE). Active compound 3c was also tested for the ability to inhibit Aβ aggregation. Theoretical physicochemical properties of the compounds were calculated using ACD Labs Percepta and Chemaxon. A Lineweaver–Burk plot and docking study showed that 3c targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Moreover, 3c appears to possess neuroprotective activity and could be considered a free-radical scavenger. In addition, 3c did not cause DNA damage and was found to be less toxic than tacrine after oral administration; it also demonstrated little inhibitory activity towards hyaluronidase (HYAL), which may indicate that it possesses anti-inflammatory properties. The screening for new in vivo interactions between 3c and known receptors was realized by yeast three-hybrid technology (Y3H).

Design and synthesis of a novel class EGFR/HER2 dual inhibitors containing tricyclic oxazine fused quinazolines scaffold

Two series of novel tricyclic oxazine and oxazepine fused quinazolines have been designed, synthesized and evaluated for their inhibitory activity against EGFR and HER2. Structure-activity relationship (SAR) of these compounds was discussed. From the SAR studies, we found that intramolecular cyclization which possessed a functional Michael acceptor group can enhance the antitumor activities. Compounds 1e and 1h were identified as lead compounds which displayed almost 3–4 times more potent inhibition of EGFR and HER2 than the approved drug lapatinib. The satisfactory physicochemical properties of these compounds were also supported by ACD labs. The results presented here will promote the development of newer dual inhibitors of EGFR and HER2.

Modeling and Molecular Docking Studies on Alangium salvifolium (Alanginaceae) as a Target for Anti-oxidant Enzyme

Objectives: The present studies pursue at retrieve and draws the active phytocompounds structure of Alangium salvifolium and assessing its simulation anti-oxidant enzyme activities.
 Methods: Retrieve/draws of the compounds were carried out using chem.-sketch software. The 3-D structures of the Phytocompounds were visualized based upon the UV, NMR spectral data along with their energy simulation studies. The antioxidant and enzyme simulation activity were evaluated in-silico using the ACD labs,PyRx, RASMOL,PYMOL,Aragslab and Discovery 3.1 studio.
 Key Findings: Phytochemicals structure drawing of A. salvifolium resulted in the structured and recognition of four phytochemicals. The plant phytochemicals showed significant anti-oxidant enzymes activity enhancer and ROS eliminator through binding to its metal domain receptor.
 Conclusion: Phytochemicals were drawing from A. salvifolium. To the best of our knowledge, among these phytochemicals, were studied anti-oxidant enzymes metals binding domain to increase the ROS scavenging activity for the foremost time from mimic with molecular docking. Moreover, study of phytochemicals simulation was for the first time from this plant. The plant revealed auspicious increase the antioxidant activities virtual screening. This gives thinking to some of its pharmacological properties and suggests additional antioxidant effects, for as a scavenger as well as anti-oxidant enzyme stimulator, which have not been reported yet.

Alternative solvents for lipid extraction and their effect on protein quality in black soldier fly (Hermetia illucens) larvae

Abstract Scrutiny of alternative solvents for the extraction of lipid constituents from black soldier fly (BSF) was the main theme of this research. The present investigation compared a wide array of solvents for the extraction of desired components theoretically using tools like Hansen solubility parameters (HSP), conductor-like screening model for real solvents (COSMO-RS) and technical data (ACD labs) with the application of hurdle technology for solvent screening. The ideal solvent selected was 2-methyloxolane (2-MeO) which was employed for conventional and multistage cross-current lipid extraction and the experimental data obtained was compared with that of n-hexane extract. Fatty acid profile, lipid class, bioactivity of the oils were analysed and were in good correlation with the theoretical prediction. The kinetics and diffusion modelling for the extraction system was proposed. The effect of solvent on protein quality parameters like protein dispersibility index, solubility in alkaline solution, urease index in the defatted flour was elucidated. The defatting step had no deleterious effect on the molecular weight distribution of soluble proteins. Overall the study manifested that 2-MeO had better lipid recovery, enhanced bioactivity in the BSF oil, and relatively better protein quality in the defatted flour.

СПЕКТОРОФОТОМЕТРИЧНІ ТА ПРОТОЛІТИЧНІ ВЛАСТИВОСТІ КОНДЕНСОВАНИХ ЦІАНОПІРИДИНІВ

Development of new optical probes is a promising trend that has been actively implemented in recent years. A rational design of the probes should consider a number of parameters that contribute to the ability of the probe to exhibit highly selective optical response to the analyte. The obvious criteria are the chemical stability and reactivity of the probe, its photostability and the possibility of its reusable application. In this work, new probes based on fused benzothiazoles with different heterocyclic substituents were studied. The spectrophotometric characteristics of compounds in dimethylsulfoxide, acetonitrile and ethanol solutions were obtained. The probes exhibited the absorption in the near UV region and the blue part of the visible spectrum. Absorption spectra of the molecules are characterized by broad band with absorption maximum around 391–400 nm. The selected compounds demonstrated a slight positive solvatochromism. The blue shift of absorption maxima is due to the formation of protonated form of the probe in the presence of hydrochloric acid. Further, in basic conditions, the absorbance maxima of the probes are localized at longer wavelength (Δλ around 80 nm). Reversibility of compounds in the reactions of deprotonation-protonation was studied. Formal protonation constants of compounds (lgKpf) in water-organic solutions were calculated using the UV-Vis spectrophotometry titration method. Protonation constants of probes are in the range: lgKpf = 2.67–4.95. The obtained values of the protonation constants are in good agreement with the data calculated using the software ACD Labs. The presence of the amidine fragment in the structure of the chromophore core leads to an increase in its basicity, with respect to heterocyclic substituents. It was shown that the presence of a substituent more basic than benzothiazole leads to the destruction of the probe in solution with a pH 11. It occurs due to the opening of the iminopyridine cycle into its synthetic precursor. Based on the results, 2-(1,3-benzothiazol-2-yl)-3-(3-hydroxypropyl)-1-imino-1H-pyrido[2,1-b][1,3]benzothiazole-4-carbonitrile was selected for further use as sensitive pH probe.

DESIGN AND SCREENING OF GALLIC ACID DERIVATIVES AS INHIBITORS OF MALARIAL DIHYDROFOLATE REDUCTASE (DHFR) BY IN SILICO DOCKING

Objective: Malaria is an infection disease caused by plasmodium parasite with high prevalence in tropic and subtropic countries. The aim of this work was to design and screening of gallic acid derivatives as inhibitors of malarial dihydrofolate reductase (DHFR) by in silico docking.Methods: The derivatives were designed by expanding the carboxyl group of gallic acid with open-chain moiety of L-threonine-allyl esters, as well as to modify the hydroxy groups on the aromatic ring of gallic acid with methoxyl group in the derivatives. In silico approach has been utilized in finding the potential antimalaria of gallic acid derivatives. Fourteen Gallic acid derivatives (compound 2-15) were modeled into 3D structures by ACD Labs software. Geometry optimization and minimization of energy 3D structure of gallic acid derivatives as ligands using the MOE software. Docking process and amino acid analysis were executed by using MOE software. Results: In silico docking study resulted in the three top-ranked compounds, namely compound 5, 8 and 12. Among those three top-ranked compounds, compound 12 (octyl gallate), exhibited the strongest interaction and greatest inhibitory activity against the receptor of malarial DHFR.Conclusion Our results clearly demonstrated that compound 12 (octyl gallate) could be developed as a promising candidate for the new anti-malarial agent.

A quantitative threshold for high/low extent of urinary excretion of compounds in humans.

In this study, a quantitative threshold was determined for the high/low extent of urinary excretion (UE) of compounds in humans, using a straightforward but robust statistical method known as receiver operating characteristic curve (ROC) analysis, and also 18 potential physicochemical determinants of UE were evaluated. Data on the percent of drug excreted unchanged into the urine, %Ae , were used to determine the threshold for high/low UE. Compounds can be divided into high/low UE groups using the threshold value of Ae =16.8%, namely those with Ae >16.8% are classified as high UE and those with Ae ≤16.8% as low UE. The %Ae negatively correlated with cLogP (r=-0.56); however, cLogP could not quantitatively predict the value of %Ae (R(2) adj. = 0.32). Several determinants of the extent of UE, including cLogP, ACD labs cLogP and ACD labs cLogD(pH=7.4) , were successfully evaluated as a priori indicators of the extent of UE using two cut-off values for each parameter. Moreover, 87% of the 90 compounds in the external validation set were correctly classified using this approach. Analysis of the physicochemical spaces of compounds in these two groups showed significant overlap, which hinders the a priori determination of the extent of UE of compounds using a single threshold/cut-off value of simple physicochemical parameters. In conclusion, 16.8% is a quantitative threshold value to distinguish between high and low UE and new molecular entities with cLogP and ACD labs cLogP values of ≤0.7 and ≥1.0 and ACD labs cLogD(pH=7.4) values of ≤0.0 and ≥0.5 could be identified as exhibiting high and low UE, respectively. Copyright © 2016 John Wiley & Sons, Ltd.

Chemometric-assisted determination of some bisphosphonates and their related substances in pharmaceutical forms by ion chromatography with inverse UV detection

A simple ion chromatographic (IC) method was developed and validated for simultaneous or individual determination of zoledronic, alendronic, pamidronic acids and their related substances in pharmaceutical formulation. The analytes were separated on Waters IC-Pak Anion HR analytical column with a nitric acid (3 mM) without any other additives, as mobile phase at a flow rate of 1.0 mL min−1. Inverse UV detection was used at 240 nm. Important chromatographic factors that influence the chromatography responses were screened by 11/12 Pluckett–Burman design and their interaction were assayed by 23 full factorial design. The RP-HPLC method was optimized with the aid of LC-Simulator® (ACD Labs, Toronto, Ontario, Canada) software. Validated method was successfully used for quantitative analysis of PAMIFOS®, concentrate for infusion (Habitfarm AD, Ivanjica, Serbia), ZOMETA®, powder for infusion (Novartis Pharma, Stein AG, Switzerland) and BONAP® tablets (Hemofarm, Vrsac, Serbia). Total chromatographic analysis time...

Analysis and Detection of Scytophycin Variants by HPLC-ESI-MS

A significant number of cyanobacteria possess interesting biological activities, including cytotoxic [1] and, rarely, fungicidal [2]. One of the most potent group of this are scytophycins, found in cyanobacteria of the family Scytonemataceae 30 years ago [3]. The best known representative of the scytophycin family, tolytoxin (6-hydroxy-7-O-methylscytophycin B), was first isolated from a terrestrial blue-green alga Tolypothrix conglutinata [4]. The genus Nostoc is a rich source of various bioactive metabolites, but scytophycins were never observed to be produced by this cyanobacterium. In this study we apply LCMSn instrumentation in order to extend its applicability for structural analysis of the scytophycin family members. The crude 70% MeOH extract of the soil cyanobacterium Nostoc sp. 5/96 exhibited strong antifungal and cytotoxic activity. Activity-guided fractionation led to a discovery of several active fractions ranging from 20 to 30 min of the MeOH–H2O gradient (Zorbax XBD C8, 46 150 mm, 5 m). Eight peaks were detected in this region by ESI-MS in the positive mode (Table 1). We deduced that these ions can be sodium adducts of the scytophycin macrolides. Molecular ions were not intense enough even after addition of buffer, but the fragmentation of Na+ adducts was convincing. Generally, methylation of hydroxyl groups increases retention time, and more free hydroxyl groups lower the retention time (Table 1). Retention also corresponds well with log P values: for the scytophycin B family: 1.28, –0.42, 0.26, 1.04; and for the scytophycin D/E families: –0.66/–0.80, 0.20/0.06, 0.88/0.74. The values of log P were calculated using ACD Labs software. For distinguishing several scytophycins of the same mass that appeared in our sample (e.g., m/z 845, 843, 859, 875), MS/MS was necessary. Additionally, the shifting technique [6] was applied. Support in elucidating the structure of the fragments was obtained by using the ACD/MS Fragmenter.

Chemometric-Assisted Optimization of RP-HPLC Method for Determination of Some Bioflavonoids in Brassica oleracea Species and Their Antioxidative Activity

In the present work, the rapid RP-HPLC method with UV (DAD) detection for simultaneous quantification of bioflavonoids: quercetin, apigenin, catechin, epicatechin, kaempferol, and luteolin in Brassica oleracea species samples (cauliflower, broccoli, and Brussels sprouts) was developed with the aid of LC-Simulator (ACD Labs® suite) software. A series of extracts obtained with different extraction method were evaluated for antioxidant activity. The optimal conditions for separation and quantification were established after nine scouting runs entered to LC-Simulator software. The optimized separation was achieved on Hypersil GOLD aQ column with isocratic elution and mobile phase composition A:2 % acetic acid in water and B:acetonitrile in 91:9 (v/v %) ratio. The Rs values were in the range from 2.6 to 8.00, indicating good selectivity of the method. The obtained results generally show good agreement with published data. Low detection limits (0.02–0.055 μg/mL) were obtained with acceptable recoveries (90–109 %). Total time of analysis was less than 11 min; therefore, the proposed method represents significant improvement over existing methods. Extracts from Brassica vegetables, obtained using different extraction procedures, were studied for their radical scavenging effects. Scavenging of DPPH showed different kinetics at the beginning of the assay period and after 15 min from the initialization of reaction. Different kinetics suggested the presence of polymerized and/or less active antioxidants with different scavenging mechanisms for particular polyphenolic compounds.

Exploring the interplay of physicochemical properties, membrane permeability and giardicidal activity of some benzimidazole derivatives

This study evaluated the relationship between the physicochemical properties, membrane permeability and in vitro giardicidal activity of twenty nine benzimidazole derivatives (1–7n). The retention time data from reverse phase high performance chromatography (RP-HPLC) were used to estimate aqueous solubility and lipophilicity of these compounds. The apparent permeability was determined using Caco-2 cell monolayer. The calculation of some descriptors, such as Clog P, PSA, was performed using ACD labs software. For benzimidazole derivatives with NHCOOCH3, CH3, NH2, SH and SCH3 groups at the 2-position, a quadratic type of regression model was obtained with giardicidal activity and aqueous solubility or lipophilicity. On the other hand, giardicidal activity of 2-(trifluoromethyl)-1H-benzimidazole derivatives was influenced by lipophilicity, hydrogen bond donors and molecular volume but it was not determined by their apparent permeability in Caco-2 cell line.

Potential 1H NMR urinary metabolomic biomarkers for Lung cancer in hamster model

The objective of this study was to use the metabolomic approach to investigate early potential biomarkers for lung cancer. Golden Syrian hamsters were randomized into 2 groups. Lung cancer was induced in treatment group by a chemical carcinogen, N‐nitrosobis‐2‐(oxopropyl) amine (BOP). Proton nuclear magnetic resonance (1H NMR) spectra, acquired using 500 MHz magnet were processed using ACD labs software. The processed, digitized NMR spectral data was analyzed using multivariate data analysis software, SIMCA P+. Principal Component Analysis (PCA) score plots showed significant separation between the cancer and control groups. The metabolites responsible for the differences between the two groups as observed from the PCA loading plots, were quantified using CHENOMX NMR metabolite database. The metabolites (n=26) found to be significantly different in the two groups were traced back to their respective biochemical pathways in an effort to gain mechanistic insight into lung cancer progression from the metabolite view point. Some of these metabolites such as glycine, sarcosine, and alanine have been previously reported to be increased in other cancer types. These could potentially serve as potential biomarkers of cancer in general. In addition, some metabolites may be of specific relevance to progression of lung cancer and may therefore be further explored as possible biomarkers of this aggressive cancer type.Grant Funding Source: This work was funded by start up funds from Wayne State University.

Differentiation of structural isomers in a target drug database by LC/Q‐TOFMS using fragmentation prediction

Isomers cannot be differentiated from each other solely based on accurate mass measurement of the compound. A liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOFMS) method was used to systematically fragment a large group of different isomers. Two software programs were used to characterize in silico mass fragmentation of compounds in order to identify characteristic fragments. The software programs employed were ACD/MS Fragmenter (ACD Labs Toronto, Canada), which uses general fragmentation rules to generate fragments based on the structure of a compound, and SmartFormula3D (Bruker Daltonics), which assigns fragments from a mass spectra and calculates the molecular formulae for the ions using accurate mass data. From an in-house toxicology database of 874 drug substances, 48 isomer groups comprising 111 compounds, for which a reference standard was available, were found. The product ion spectra were processed with the two software programs and 1-3 fragments were identified for each compound. In 82% of the cases, the fragment could be identified with both software programs. Only 10 isomer pairs could not be differentiated from each other based on their fragments. These compounds were either diastereomers or position isomers undergoing identical fragmentation. Accurate mass data could be utilized with both software programs for structural elucidation of the fragments. Mean mass accuracy and isotopic pattern match values (SigmaFit; Bruker Daltonics Bremen, Germany) were 0.9 mDa and 24.6 mSigma, respectively. The study introduces a practical approach for preliminary compound identification in a large target database by LC/Q-TOFMS without necessarily possessing reference standards.

Evaluation of Peakmaster for computer‐aided multivariate optimisation of a CE separation of 17 antipsychotic drugs using minimal experimental data

The computer-assisted development of a CE method for compliance monitoring of a group of 17 antipsychotic drugs (chlorpromazine hydrochloride, clozapine, droperidol, flupenthixol dihydrochloride, fluphenazine dihydrochloride, haloperidol, pimozide, thioridazine hydrochloride, trifluoperazine dihydrochloride, prochlorperazine dimaleate, amisulpride, aripiprazole, olanzapine, quetiapine fumarate, risperidone, ziprasidone, and zuclopenthixol dihydrochloride) was performed. Peakmaster, a free simulation program for CE, was employed in a multivariate optimisation approach to determine suitable BGE conditions with minimal experimentation. However, analyte input parameters (pK(a) and limiting ionic mobility) were not included within the software and required determination. Limiting ionic mobility was determined experimentally, while pK(a) values were calculated using ACD Labs software. A modified chromatographic response factor, which identified the BGE providing the greatest resolution between each pair of peaks within 10 min, was used and determined a pH 2.5 and an ionic strength of 50 mM as optimal. Marked disparities were apparent between experimentally determined and computer-simulated results, due to error associated with pK(a) values calculated using ACD Labs. These results confirm that Peakmaster analyses are highly sensitive to pK(a) values, especially where the pH of the BGE is in the proximity of the analyte pK(a); but also that Peakmaster does allows a rational approach to dramatically reduce the amount of experimental work required for multivariate optimisation of conditions for CE.

Application of log D for the prediction of hydrophobicity in the advanced Marfey's method

In the advanced Marfey's method, the resolution between the diastereomers derivatized with 1-fluoro-2,4-dinitrophenyl-5- l-leucinamide ( l-FDLA) and 1-fluoro-2,4-dinitrophenyl-5- d-leucinamide ( d-FDLA) is reflected by the difference of hydrophobicity of the two functional groups at the asymmetric carbon. However, no effective method has been developed for the estimation of hydrophobicity so far. For this purpose, we introduced log D from the ACD Labs LogD and applied it to relatively simple primary amines, amino acids and secondary alcohols in the present study. It was found that the difference of the retention times (Δ t R) correlated with that of log D (Δlog D) for both diastereomers based on the obtained experimental results. Based on these results, the following procedure was proposed for the non-empirical determination of the absolute configuration of primary amines including amino acids and secondary alcohols: (1) estimate the hydrophobicity by the calculation of log D for the two substituent groups at the asymmetric carbon, (2) locate the trans-type arrangement of the two more hydrophobic substituents in the l-DLA derivative and judge the asymmetric carbon to be R or S in the trans-type that is eluted first, (3) derivatize the desired compound with l- or d-FDLA and analyze by LC/MS, and (4) compare the elution order with the prospective one and determine the absolute configuration at the asymmetric carbon. Furthermore, log D could also be used to predict the retention times of unavailable amino acids and small peptides, indicating that the combination of the advanced Marfey's method with log D would provide more reliable structural information on a mixture composed of amino acids and small peptides. The developed method is being applied to more complicated compounds.

Rapid determination of the applicability of hydrophilic interaction chromatography utilizing ACD Labs Log D Suite: A bioanalytical application

Hydrophilic interaction chromatography (HILIC) is an effective technique for retaining and separating polar compounds. This approach offers several advantages for bioanalytical liquid chromatography/mass spectrometry, considering that a majority of active pharmaceutical ingredients are polar amines. HILIC employs high concentrations of relatively polar organic mobile phase components (i.e. acetonitrile), providing enhanced desolvation and electrospray ionization efficiency, as well as allowing direct injection of many protein precipitation, liquid/liquid, and solid phase extracts. A set of 30 probe compounds was evaluated to demonstrate a relationship between a compound's HILIC capacity factor ( k′), and pH dependent distribution coefficient ( D), using three sets of generic isocratic conditions. Plots of log k′ versus log D pH 3.0 produced correlation coefficients of 0.751, 0.696, and 0.689 at acetonitrile mobile phase concentrations of 85%, 90%, and 95% (v/v), respectively. For bioanalytical applications a k′ > 2 is typically targeted to ensure adequate retention of a given analyte relative to extracted matrix components. Using k′ ≥ 2 as a measure of HILIC applicability, the linear relationships for each of the three acetonitrile levels predicted whether or not HILIC was able to meet this criterion for at least 90% of the compounds tested. Overall, the relationship between k′ and log D can serve as a valuable tool for identifying the applicability of HILIC and a starting point for the chromatographic conditions, prior to the initiation of any laboratory activities. Additionally, this relationship can assist with the selection of appropriate chemical analog internal standards.