Understanding the reactivity of captodative ethylenes in polar cycloaddition reactions. A theoretical study

Understanding the different reactivity of (Z)- and (E)-β-nitrostyrenes in [3+2] cycloaddition reactions. An MEDT study

The experimental reactivity of isomeric (Z)- and (E)-β-nitrostyrenes participating in [3+2] cycloaddition (32CA) reactions has been analysed on the basis of molecular electron density theory (MEDT) at the HF/6-311G(d,p), B3LYP/6-311G(d,p) and ωB97X-D/6-311G(d,p) computational levels. It was found that the polar zw-type 32CA reactions with 5,5-dimethylpyrroline-N-oxide proceed via a one-step mechanism, characterised by the attack of the nucleophilic oxygen centre of the nitrone on the electrophilically activated β-position of these nitrostyrenes. This behaviour is completely understood by means of the analysis of the conceptual DFT reactivity indices. These 32CA reactions present low activation enthalpies of 4.4 (Z) and 5.0 (E) kcal mol-1, and are exo (Z) and endo (E) stereoselective (B3LYP), as well as completely meta regioselective (ωB97X-D, B3LYP). The less stable (Z)-β-nitrostyrene is more reactive than the (E)-one (HF). ELF and AIM topological analyses of the reagents and TSs show the great similitude between their electronic structures. Finally, NCI allows explaining the exo stereoselectivity found in the reaction of (Z)-β-nitrostyrene. The present MEDT study explains the different reactivity, selectivity and competitiveness in the title reactions.

Nucleophilicity Prediction via Multivariate Linear Regression Analysis

The concept of nucleophilicity is at the basis of most transformations in chemistry. Understanding and predicting the relative reactivity of different nucleophiles is therefore of paramount importance. Mayr’s nucleophilicity scale likely represents the most complete collection of reactivity data, which currently includes over 1200 nucleophiles. Several attempts have been made to theoretically predict Mayr’s nucleophilicity parameters N based on calculation of molecular properties, but a general model accounting for different classes of nucleophiles could not be obtained so far. We herein show that multivariate linear regression analysis is a suitable tool for obtaining a simple model predicting N for virtually any class of nucleophiles in different solvents for a set of 341 data points. The key descriptors of the model were found to account for the proton affinity, solvation energies, and sterics.

Quantum chemical study in exploring the role of donor→acceptor interactions in 1,3-bis carbene-stabilized guanidinium cations

Guanidinium species are highly basic and hence mostly exist in cationic state. Because these cations carry electron-deficient centers, they can be stabilized with the help of electron-donating ligands like N-heterocyclic carbenes. A few novel guanidinium cationic species stabilized by electron-donating ligands were designed and quantum chemically evaluated. It was shown that strong hydrogen bonds and tautomerism are the important characteristics of these species. Further, the possibility of donor→acceptor coordination interactions in these species have been explored between the electron-donating carbenes and the central guanidinium unit. The results suggest that the title compounds can be considered as ligand-stabilized guanidinium cations similar to the ligand-stabilized N⁺ and N₃⁺ centers.

Unveiling the molecular mechanisms of the cycloaddition reactions of aryl hetaryl thioketones and C,N-disubstituted nitrilimines

Many synthetic routes to constructing biologically active heterocyclic compounds are made feasible through the (3 + 2) cycloaddition (32CA) reactions. Due to a large number of possible combinations of several heteroatoms from either the three-atom components (TACs) or the ethylene derivatives, the potential of the 32CA reactions in heterocyclic syntheses is versatile. Herein, the cycloaddition reaction of thiophene-2-carbothialdehyde derivatives and C,N-disubstituted nitrilimines have been studied through density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level of theory. In the present study, a one-step 32CA and two-step (4 + 3) cycloaddition (43CA) reaction mechanisms involved in TACs reactions and ethylene derivative have been investigated. In all reactions considered, the one-step 32CA cycloaddition is preferred over the two-step 43CA. The TAC chemoselectively adds across the thiocarbonyl group present in the ethylene derivative in a 32CA fashion to form the corresponding cycloadduct. Analysis of the electrophilic [Formula: see text] and nucleophilic [Formula: see text] Parr functions at the various reaction centers in the ethylene derivative show that the TAC adds across the atomic centers with the largest Parr functions, which is in total agreement with the experimental observation. The selectivities observed in the titled reactions are kinetically controlled.

The Azide-Allene Dipolar Cycloaddition: Is DFT Able to Predict Site- and Regio-Selectivity?

The site- and regio-selectivity of thermal, uncatalysed 1,3-dipolar cycloadditions between arylazides and mono- or tetra-substituted allenes with different electronic features have been investigated by both conceptual (reactivity indices) and computational (M08-HX, ωB97X-D, and B3LYP) DFT approaches. Both approaches show that these cycloadditions follow a nonpolar one-step mechanism. The experimental site- and regio-selectivity of arylazides towards methoxycarbonyl- and sulfonyl-allenes as well as tetramethyl- and tetrafluoro-allenes was calculated by DFT transition state calculations, achieving semiquantitative agreement to both previous and novel experimental findings. From the mechanistic standpoint, 1H-NMR evidence of a methylene-1,2,3-triazoline intermediate reinforces the reliability of the computational scheme.

The origin of the regiospecificity of acrolein dimerization

Acrolein dimerization is a intriguing case since the reaction does not occur to form the electronically preferred regioisomeric adduct. Various explanations have been suggested to rationalize this experimental regioselectivity, however, none of these arguments had been convincing enough. In this work, the hetero Diels-Alder acrolein dimerization was theoretically investigated using DFT and MP2 methods. The influence of nucleophilic/electrophilic interactions and non-covalent interactions (NCI) in the regiospecificity of the reaction were analyzed. Our results show that the NCI at the transition state are the key factor controlling the regiospecificity in this reaction. Besides, we found that the choice of calculation method can have an effect on the prediction of the mechanism in the reaction, as all DFT methods forecast a one-step hetero Diels-Alder acrolein dimerization, while MP2 predicts a stepwise description for the lower energy reaction channel.

DFT Quest of the Active Species of the Gallium-Mediated Coupling of Methylidenemalonates and Acetylenes

In this study, three different Ga-containing systems based on GaCl₃, Ga₂Cl₆, or ionic [Ga(L)₃][GaCl₄]₃ (L = methylidenemalonate) complex were screened to elucidate the mechanism, regioselectivity, chemoselectivity, and role of Ga mediator in the reaction between two types of acetylenes (phenylacetylene and but-1-yn-1-ylbenzene) and methylidenemalonates, i.e., the 1,2-zwitterionic precursors that are similar to intermediates derived from donor-acceptor cyclopropanes (DACs). Our DFT calculation results clearly show that the ionic gallium complex [Ga(L)₃][GaCl₄]₃ represents the key mediator in the title reaction. After the formation of such a complex, the first reaction step is the nucleophilic addition of phenylacetylene or but-1-yn-1-ylbenzene to [Ga(L)₃][GaCl₄]₃, generating an unstable vinyl cation intermediate. In the phenylacetylene system, this vinyl cation intermediate accepts a chlorine atom from [GaCl₄]^- to give E-configuration intermediate. Then, the above process occurs to other two ligands of the Ga(III) complex to furnish a final product. On the other hand, in the but-1-yn-1-ylbenzene system, the vinyl cation intermediate prefers to undergo Friedel-Crafts (F-C) alkylation to generate a five-membered ring intermediate. This process is repeated on the other two methylidenemalonate ligands, giving rise to a final cyclization product. The distortion/interaction analysis shows that in the nucleophilic addition step the distortion energy of the Ga complex part is the main factor that influences the activation energy. Furthermore, the global reactivity index (GRI) analysis indicates that the Ga-complex model has the highest electrophilicity index ω, thus leading to the lowest energy barrier among three Ga-based models. In addition, DFT results reveal that the regioselectivity (E-configuration preference) and chemoselectivity (chloration or F-C alkylation) are mainly controlled by the steric effect rather than the electronic effect. The main findings of the present work provide a new way to analyze and rationalize various Ga-mediated reactions, which might also be extrapolated to organic transformations undergoing in the presence of aluminum and indium complexes.

Theoretical mechanistic study on the reaction of the methoxymethyl radical with nitrogen dioxide

Mechanism of the reaction of CH₃OCH₂ with NO₂ is explored theoretically at the M062X/MG3S and G4 levels. The calculated results indicate two stable association intermediates, CH₃OCH₂NO₂ (IM1) and CH₃OCH₂ONO (IM2), which can be produced by the attack of the nitrogen or oxygen atom of NO₂ to terminal carbon atom of CH₃OCH₂ without barrier involved. IM2 is found to take trans (IM2a)-cis (IM2b) conversion and isomerization to IM1, with the following stability order IM2a > IM2b > IM1. Starting from IM2a, the most feasible pathway is the direct O-NO bond cleavage leading to P1 (CH₃OCH₂O + NO) or the H-shift and O-NO bond rupture to produce P2 (CH₃OCHO + HNO), both of which have comparable contribution to the title reaction. There also involves an H-transfer from the methyl group of IM2a to the N atom with the simultaneous dissociations of the C-O and O-N bonds to produce P4 (2CH₂O + HNO). In addition, another dissociation pathway is open to IM2b which decompose to P5 (CH₂O + CH₃ONO) by the O-N and C-O bond scissions and the recombination of CH₃O and NO. Because all the intermediates and transition states involved in the above pathways lie below reactants, the CH₃OCH₂ + NO₂ reaction is expected to be rapid. Subsequent dissociation of IM1 and direct H-abstraction between CH₃OCH₂ and NO₂ are kinetically almost inhibited due to significantly high barriers. The present results can lead us to deeply understand the mechanism of the title reaction and may be helpful for understanding NO₂ combustion chemistry.

Mpro-SARS-CoV-2 Inhibitors and Various Chemical Reactivity of 1-Bromo- and 1-Chloro-4-vinylbenzene in [3 + 2] Cycloaddition Reactions

The regioselectvity and the mechanism of the (32CA) cycloadditions reactions of 1-bromo-4-vinylbenzene 1 and 1-chloro-4-vinylbenzene 2 with benzonitrile oxide 3 were investigated under the molecular electron density theory (MEDT) at the B3LYP/6-311++G(d,p) computational level. Evaluation of the ELF reveals that these zwitterionic type (zw-type) 32CA reactions take place in a two-stage one-step mechanism. This MEDT study shows that the meta isoxazolines are kinetically and thermodynamically favored over the ortho ones, these 32CA reactions being completely regioselective, in agreement with experimental outcomes. In addition, the efficiency of isoxazolines against SARS-CoV-2 have been also investigated. According to the docking analysis, the present study concludes that 5-(p-bromophenyl)-3-phenyl-2-isoxazoline (B-m) shows better interactions for the inhibition of SARS-CoV-2 in comparison to chloroquine.

N-Heterocyclic Carbenes–CuI Complexes as Catalysts: A Theoretical Insight

The electronic structures of N-heterocyclic carbenes (NHC) imidazolinylidene, thiazolinylidene, imidazolylidene, thiazolylidene, and 1,2,4-triazolylidene and their complexes with cuprous halides (CuX, X=Cl, Br, I) were investigated theoretically at the B3LYP/def2-SVP level. In contrast to other NHCs, imidazolylidene and 1,2,4-triazolylidene do not dimerize owing to the negligible coefficient of the vacant p-orbital at the carbene centre in their respective LUMOs. This is further supported by their greater thermodynamic and kinetic stabilities revealed by greater activation free energies and smaller standard free energies for their dimerization. Second-order perturbation interactions in the natural bond orbital (NBO) analysis of the NHCs indicate that six π electrons are delocalized in imidazolylidene, thiazolylidene, and 1,2,4-triazolylidene, conferring aromatic character and thereby enhancing their thermodynamic stability. NBO analysis reveals the existence of effective back bonding from a d orbital of Cu to the NHC, increasing the Wiberg bond index of the C–Cu bond to ~1.5. Owing to the large electronic chemical potential (μ) and high nucleophilicity indices, NHCs are able to transfer their electron density effectively to the cuprous halides having low μ values and high electrophilicity indices to yield stable NHC–CuI complexes. Large values of the Fukui function f(r) at the carbene centre of the NHCs and Cu atom of the NHC–CuI complexes indicate their softness. Imidazolylidene was found to be the softest, rationalizing wide use of this class of NHCs as ligands. The coordination of the NHCs to cuprous halides is either barrierless or has a very low activation free energy barrier. In the A3 reaction wherein NHC–Cu(I) complexes are used as catalyst, the reaction of NHC–CuI with phenylacetylene changes the latter into acetylide accompanied by raising the energy level of its HOMO considerably compared with the level of the uncomplexed alkyne, making its reaction with benzaldehyde barrierless.

A molecular electron density theory study for [3+2] cycloaddition reactions of N-benzylcyclohexylnitrone with methyl-3-butenoate

The [3+2] cycloaddition (32CA) reactions of N-benzylcyclohexylnitrone 1 with methyl-3-butenoate 2 have been studied within molecular electron density theory (MEDT) at the B3LYP/6-311++G(d,p) level of theory.

Theoretical insight into the opposite redox activity of iron complexes toward the ring opening polymerization of lactide and epoxide

The origin of opposite reactivity in the ring-opening polymerization of lactide (LA) and cyclohexene oxide (CHO) catalyzed by redox-switchable bis(imino)pyridine iron complexes has been computationally elucidated.

Theoretical insight into the origins of chemo- and diastereo-selectivity in the palladium-catalysed (3 + 2) cyclisation of 5-alkenyl thiazolones

The mechanism of the palladium-catalysed (3 + 2) cyclisation of 5-alkenyl thiazolones and VECs has been investigated from a computational perspective, and the origins of unique chemoselectivity and excellent diastereoselectivity have been disclosed.

Unveiling the regioselectivity in electrophilic aromatic substitution reactions of deactivated benzenes through molecular electron density theory

Regioselectivity results from the slight polarization of the electron density and weak repulsive interactions appearing along the ortho approach mode.

Mechanistic study on the NHC-catalyzed [3+4] annulation of enals and thiazolones

Reaction mechanisms and origins of regio- and stereo-selectivities of NHC catalyzed [3+4] annulation of enals and thiazolones.

Rationalization of the mechanism and chemoselectivity of versatile Au-catalyzed reactions of diazoesters with allyl-functionalized sulfides, selenides, amines, or ethers by DFT

The origin of chemoselectivity and the mechanism of the title reactions were fully rationalized by density functional theory (DFT).

A theoretical study of the hydroboration of α,β-unsaturated carbonyl compounds catalyzed by a metal-free complex and subsequent C–C coupling with acetonitrile

Herein, the density functional theory (DFT) method was employed to investigate the reaction mechanism of the selective hydroboration of α,β-unsaturated carbonyl compounds catalyzed by the metal-free complex 1,3,2-diazaphospholene (DAP).

Participation of Phosphorylated Analogues of Nitroethene in Diels–Alder Reactions with Anthracene: A Molecular Electron Density Theory Study and Mechanistic Aspect

The structure and the contribution of the bis(2-chloroethyl) 2-nitro 1a and 2-bromo-2-nitroethenylphosphonates 1b with anthracene 2 in the Diels–Alder (DA) reactions have been studied within the Molecular Electron Density Theory (MEDT) at the B3LYP functional together with 6-31G(d), 6-31+G(d) and 6-31+G(d,p) basic sets. Analysis of the Conceptual Density Functional Theory (CDFT) reactivity indices indicates that 1a and 1b can be classified as a strong electrophile and marginal nucleophile, while 2 is classified as a strong electrophile and strong nucleophile. The studied DA reactions take place through a one-step mechanism. A Bonding Evolution Theory (BET) of the one path associated with the DA reaction of 1a with 2 indicates that it is associated with non-concerted two-stage one-step mechanism. BET analysis shows that the first C2-C3 single bond is formed in Phase VI, while the second C1-C6 single bond is formed in the Phase VIII. The formation of both single bonds occurs through the merging of two C2 and C3, C1 and C6 pseudoradical centers, respectively.

Understanding the Origin of the Regioselectivity in Non-Polar [3+2] Cycloaddition Reactions through the Molecular Electron Density Theory

The regioselectivity in non-polar [3+2] cycloaddition (32CA) reactions has been studied within the Molecular Electron Density Theory (MEDT) at the B3LYP/6-311G(d,p) level. To this end, the 32CA reactions of nine simplest three-atom-components (TACs) with 2-methylpropene were selected. The electronic structure of the reagents has been characterized through the Electron Localisation Function (ELF) and the Conceptual DFT. The energy profiles of the two regioisomeric reaction paths and ELF topology of the transition state structures are studied to understand the origin of the regioselectivity in these 32CA reactions. This MEDT study permits to conclude that the least electronegative X1 end atom of these TACs controls the asynchronicity in the C−X (X=C, N, O) single bond formation, and consequently, the regioselectivity. This behaviour is a consequence of the fact that the creation of the non-bonding electron density required for the formation of the new single bonds has a lower energy demand at the least electronegative X1 atom than at the Z3 one.

Coupling-oxidation process promoted ring-opening degradation of 2-mecapto-5-methyl-1,3,4-thiadizaole in wastewater

As an important raw material and intermediate of widely used antibiotics cefazolin and cefazedone, 2-mecapto-5-methyl-1,3,4-thiadizaole (MMTD) in antibiotic wastewater is hardly decyclized during wastewater treatment, posing great risk to the environment. This work proposed a green "coupling-oxidation" process to enhance ring-opening of MMTD during antibiotic wastewater treatment. In particular, the significant role of humic substances (HS) as pre-coupling reagent was emphasized. Real HS and different model HS, especially quinones, not only efficiently pre-coupled MMTD (>95%) but also promoted the MMTD removal by MnO₂ (from 72.4% to 92.4%). Mass spectrometric analysis indicated that MMTD pre-coupled to HS would be oxidized with ring opening to environmental-friendly sulfonated HS, while direct oxidation of MMTD produced MMTD dimers or sulfonated MMTD that would not undergo ring opening. Theoretical calculations indicated that pre-coupling to HS enabled the ring-opening oxidation by increasing the nucleophilicity and decreasing ring-opening barrier of thiadiazole. Based on the density function theory (DFT), the global nucleophilicity index (Nu) followed the trend of HS-MMTD > MMTD dimer > sulfonated MMTD, while the ring-opening barrier followed the trend of HS-MMTD (274 kJ/mol) < first ring of MMTD dimers (286 kJ/mol) < MMTD (338 kJ/mol). Theoretical calculations further confirmed that the cross-coupled HS-MMTD intermediate was more likely to be decyclized than intermediates from direct oxidation. Moreover, nitrogen, acetaldehyde group, sulfate and CO₂ were the products of thiadiazole ring degradation. Pre-coupling of MMTD with HS provides a new idea and strategy in developing a green and sustainable scheme for wastewater treatment.

A theoretical investigation into novel germylenes: effects of nitrogen substitution on stability and multiplicity

The effects of substituting nitrogen atoms on the stability of novel singlet (s) and triplet (t) forms of germylenes (1-20) are compared and contrasted, at B3LYP/AUG-cc-pVTZ level of theory. Every one of the 40 new divalents scrutinized appears as a minimum on its energy surface, for showing no negative force constant. Also, every singlet (1_s-20_s) appears more stable than its corresponding triplet (1_t-20_t). The highest stability (ΔE_s-t) is achieved by germylene (11) where all the three nitrogens are bonded to the central boron atom. The E_HOMO slightly decreases when the number of electronegative, σ-acceptor nitrogen atoms increases, and also causes it to be less electron-rich. Germylene 16_s with low stability (ΔE_s-t = 17.19 kcal/mol), bond gap (ΔE_HOMO-LUMO = 57.46 kcal/mol^-1), and atomic charge on -G̈e- (+ 0.9012), has high electrophilicity (ω = 3.78 eV) and nucleophilicity (N = 3.87 eV). Germylenes 8_s, 14_s, and 19_s with coordinate covalent bond between nitrogen (N(Y)) and germylene center have low ω and high ΔE_HOMO-LUMO. The purpose of the present work was, therefore, to assess the influence of nitrogen substituents on the stability (ΔΕ_s-t), band gaps (ΔΕ_HOMO-LUMO), N, ω, and heat of hydrogenation (ΔE_H). This investigation is aimed to introduce novel germylenes that can be applied as cumulated multi-dentate NHG̈e ligands.

Understanding the Reactivity of Trimethylsilyldiazoalkanes Participating in [3+2] Cycloaddition Reactions towards Diethylfumarate with a Molecular Electron Density Theory Perspective

A Molecular Electron Density Theory (MEDT) study is presented here for [3+2] cycloaddition (32CA) reactions of three trimethylsilyldiazoalkanes with diethyl fumarate. The presence of silicon bonded to the carbon of these silyldiazoalkanes changes its structure and reactivity from a pseudomonoradical to that of a zwitterionic one. A one-step mechanism is predicted for these polar zw-type 32CA reactions with activation enthalpies in CCl4 between 8.0 and 19.7 kcal·mol−1 at the MPWB1K (PCM)/6-311G(d,p) level of theory. The negative reaction Gibbs energies between −3.1 and −13.2 kcal·mole−1 in CCl4 suggests exergonic character, making the reactions irreversible. Analysis of the sequential changes in the bonding pattern along the reaction paths characterizes these zw-type 32CA reactions. The increase in nucleophilic character of the trimethylsilyldiazoalkanes makes these 32CA reactions more polar. Consequently, the activation enthalpies are decreased and the TSs require less energy cost. Non-covalent interactions at the TSs account for the stereoselectivity found in these 32CA reactions involving the bulky trimethylsilyl group.

Lithium Cation-Catalyzed Benzene Diels-Alder Reaction: Insights on the Molecular Mechanism Within the Molecular Electron Density Theory

The lithium cation Li⁺-catalyzed Diels-Alder (DA) reactions of benzene toward a series of acetylenes of improved nucleophilicity can be described within the context of the molecular electron density theory (MEDT) at the ωB97XD/6-311G(d,p) level. Conceptual density functional theory indices characterize the crown ether solvated complex benzene-lithium Bz-Li-Cro as a superelectrophile. Coordination of a lithium cation to benzene does not change substantially the electron localization function electronic structure of benzene. The DA reaction of Bz-Li-Cro with acetylene shows a reduction of the energy of activation of 6.9 kcal·mol^-1, which is not sufficient for the reaction to take place, thus demanding the participation of strong nucleophilic acetylenes. DA reactions of complexes Bz-M-Cro (M = Li, Na, and K) are decelerated with the decrease of the ionization potential of the alkali metal. The one-step mechanism of these lithium cation Li⁺-catalyzed DA reactions changes to a two-step one for the reaction with dimethyl propynamine. The present MEDT study proves that analysis of the electrophilicity and nucleophilicity indices is an excellent tool for experimental organic chemists to understand, even to predict, the chemical organic reactivity.

Design, Synthesis, and Bioevaluation of Substituted Phenyl Isoxazole Analogues as Herbicide Safeners

Herbicide safeners enhance herbicide detoxification in crops without affecting target weed sensitivity. To enhance crop tolerance to the toxicity-related stress caused by the herbicide acetochlor (ACT), a new class of substituted phenyl isoxazole derivatives was designed by an intermediate derivatization method as herbicide safeners. Microwave-assisted synthesis was used to prepare the phenyl isoxazole analogues, and all of the structures were confirmed via IR, ¹H NMR, ¹³C NMR, and HRMS. Compound I-1 was further characterized by X-ray diffraction analysis. Bioassay results showed that most of the obtained compounds provided varying degrees of safening against ACT-induced injury by increasing the corn growth recovery, glutathione content, and glutathione S-transferase activity. In particular, compound I-20 showed excellent safener activity against ACT toxicity, comparable to that of the commercial safener benoxacor. Gaussian calculations have been performed and the results indicated that the nucleophilic ability of compound I-20 is higher than that of benoxacor, thus the activity is higher than that of benoxacor. These findings demonstrate that phenyl isoxazole derivatives possess great potential for protective management in cornfields.

Unprecedented Regio- and Stereoselective Synthesis of Pyrene-Grafted Dispiro[indoline-3,2'-pyrrolidine-3',3″-indolines]: Expedient Experimental and Theoretical Insights into Polar [3 + 2] Cycloaddition

A series of dispiro[indoline-3,2'-pyrrolidine-3',3″-indolines] was synthesized via a multicomponent polar [3 + 2] cycloaddition (32CA) reaction of isatin derivatives, sarcosine and (E)-3-(2-oxo-2-(pyren-1-yl)ethylidene)indolin-2-one derivatives. The regio- and stereochemistries of the cycloadducts were established on the basis of one-dimensional (1D) (1H-, 13C-, 13C-CRAPT NMR) and two-dimensional (2D) homonuclear and heteronuclear correlation NMR spectrometry experiments (1H-1H gDQFCOSY, 13C-1H-HSQCAD, 13C-1H-HMBCAD, 1H-1H-ROESYAD). The molecular mechanism and regio- and stereoselectivities of the cycloaddition (CA) reaction have been investigated utilizing a density functional theory (DFT) method and were thoroughly explained based on the transition-state stabilities and global/local electrophilicity/nucleophilicity reactivity indices of the reactants.

Virtual Screening of Marine Natural Compounds by Means of Chemoinformatics and CDFT-Based Computational Peptidology

This work presents the results of a computational study of the chemical reactivity and bioactivity properties of the members of the theopapuamides A-D family of marine peptides by making use of our proposed methodology named Computational Peptidology (CP) that has been successfully considered in previous studies of this kind of molecular system. CP allows for the determination of the global and local descriptors that come from Conceptual Density Functional Theory (CDFT) that can give an idea about the chemical reactivity properties of the marine natural products under study, which are expected to be related to their bioactivity. At the same time, the validity of the procedure based on the adoption of the KID (Koopmans In DFT) technique, as well as the MN12SX/Def2TZVP/H2O model chemistry is successfully verified. Together with several chemoinformatic tools that can be used to improve the process of virtual screening, some additional properties of these marine peptides are identified related to their ability to behave as useful drugs. With the further objective of analyzing their bioactivity, some useful parameters for future QSAR studies, their predicted biological targets, and the ADMET (Absorption, Distribution, Metabolism, Excretion and Toxicity) parameters related to the theopapuamides A-D pharmacokinetics are also reported.