Organotin Compound Derived from 3-Hydroxy-2-formylpyridine Semicarbazone: Synthesis, Crystal Structure, and Antiproliferative Activity

The novel diphenyltin(IV) compound [Ph2(HyFoSc)Sn] (2), where H2HyFoSc (1) is 3-hydroxy-2-formylpyridine semicarbazone, was prepared and characterized by vibrational and NMR (1H, 13C) spectroscopy. The structure of [Ph2(HyFoSc)Sn] was confirmed by single-crystal X-ray crystallography. The doubly deprotonated ligand is coordinated to the tin atom through the enolic-oxygen, the azomethine-nitrogen, and phenolic-oxygen, and so acts as an anionic tridentate ligand with the ONO donors. Two carbon atoms complete the fivefold coordination at the tin(IV) center. Intermolecular hydrogen bonding, C–H → π, and π → π interactions combine to stabilize the crystal structure. Compounds 1 and 2 have been evaluated for antiproliferative activity in vitro against the cells of three human tumor cell lines: MCF-7 (human breast cancer cell line), T24 (bladder cancer cell line), A549 (nonsmall cell lung carcinoma), and a mouse fibroblast L-929 cancer cell line

Stable Hemiaminals: 2-Aminopyrimidine Derivatives

Stable hemiaminals can be obtained in the one-pot reaction between 2-aminopyrimidine and nitrobenzaldehyde derivatives. Ten new hemiaminals have been obtained, six of them in crystal state. The molecular stability of these intermediates results from the presence of both electron-withdrawing nitro groups as substituents on the phenyl ring and pyrimidine ring, so no further stabilisation by intramolecular interaction is required. Hemiaminal molecules possess a tetrahedral carbon atom constituting a stereogenic centre. As the result of crystallisation in centrosymmetric space groups both enantiomers are present in the crystal structure

Why Is the Resolution of Certain Racemic Modifications Inefficient? Formation of Diastereomeric Double Salts of Brucinium

Fractional crystallization of diastereomeric salts remains the most frequently used method for a separation of racemic compounds, and yet it has been performed by trial and error. For a better understanding of the chiral discrimination mechanism that is useful for the rationalization of optical resolution and help in choosing the crucial experimental parameters, structural investigations of products of both successful and unsuccessful racemic resolution are important. The former and the latter typically involve diastereomeric salts precipitating fractionally and the formation of solid solutions of diastereomeric salts or diastereomeric double salts, respectively. In this contribution, a mechanism of recognition leading to formation of the diastereomeric double salts is proposed based on crystal structures of three brucinium double salts (bis­(brucinium) <i>N</i>-(3,5-dinitrobenzoyl)-dl-alaninate methanol 3-solvate, bis­(brucinium) <i>N</i>-(3,5-dinitrobenzoyl)-dl-alaninate 5.75-hydrate, and bis­(brucinium) <i>N</i>-(3,5-dinitrobenzoyl)-dl-serinate 0.10-hydrate) as well as of some relevant diastereomeric salts (containing the d- or l-enantiomer of the alanine or the serine derivative)

Stable Hemiaminals with a Cyano Group and a Triazole Ring

Under neutral conditions the reactions between 4-amino-1,2,4-triazole and cyano-substituted benzaldehyde derivatives yield stable hemiaminals. Addition of small amounts of acid catalyst promotes further step of dehydration resulting in formation of Schiff bases. Four new hemiaminals and the corresponding imines have been obtained. The molecular stability of the hemiaminal intermediates results from both the 1,2,4-triazole moiety and electron withdrawing substituents on the phenyl ring, so no further stabilisation by intramolecular interaction is required. Hemiaminal molecules possess stereogenic centres on carbon and nitrogen atoms. The chirality of these centres is strongly correlated with the conformation of the molecules due to heteroatom hyperconjugation effects

Dielectrically Controlled Priority of Interactions in Molecular Recognition

It was shown previously that formation of brucinium double salts during attempts of racemic resolution of <i>N</i>-(3,5-dinitrobenzoyl)­amino acid (alanine or serine) by fractional crystallization of brucinium diastereomeric salts is related to the self-recognition of anions of the amino acid derivatives into dimeric units stabilized by a set of hydrogen bonds (Białońska, A. and Ciunik, A. Why Is the Resolution of Certain Racemic Modifications Inefficient? Formation of Diastereomeric Double Salts of Brucinium. <i>Cryst. Growth Des.</i> <b>2013</b>, <i>13</i>, 111−120). Similar dimeric units were observed in brucinium diastereomeric salts precipitated from methanol solutions containing brucine and one enantiomer of the amino acid derivative. To test if the ability of the anions to form dimeric units can be weakened, an increase of dielectric constant of solutions from which the brucinium salts precipitated was applied. In this approach, three new crystalline forms of brucinium salts with enantiomeric <i>N</i>-(3,5-dinitrobenzoyl)­serine were obtained. Two of them belong to Z’ > 1 structure, and occurrence of the Z’ > 1 structures is discussed. In the new crystalline forms, a set of hydrogen bonds that stabilizes the dimeric units is replaced by interactions of the anions with solvent molecules, and the anions are linked to each other at most by lone hydrogen bonds. Recognition between cationic and anionic species by ionic N–H⁺···O^– hydrogen bonds, observed in the previously reported crystal structures of brucinium <i>N</i>-(3,5-dinitrobenzoyl)-l-serinate 3.88-hydrate and in the new form, brucinium <i>N</i>-(3,5-dinitrobenzoyl)-l-serinate brucine 11.5-hydrate, is precluded by formation of π···π stacking interactions between the anions and brucine molecules as well as by separation of the anions and cations by the extended net of hydrogen-bonded water molecules

Seventeen-Membered Water Cluster Resulting from Recognition of Solvated Anions on Brucinium Corrugated Layers

Formation of diastereomeric salts remains the most important method for the separation of racemic acids and bases. Selection of a suitable resolving agent in this method is a key for successful resolution. There are primary, secondary, and tertiary chiral amines among frequently used resolving agents for the separation of racemic acids. Cations of most of them and anions of resolved acids are linked to each other by a characteristic system of hydrogen bonds resulting in common cationic–anionic self-assemblies. In this respect, brucine and strychnine are unique, because incorporation of anionic species into a crystal lattice of their salts usually does not affect common cationic self-assembly. The uniqueness of both resolving agents is also reflected in a high frequency of solvated salt formation. In this paper, we show that the presence of water molecules incorporated into the crystal lattice of the brucinium salt may result from recognition of the resolved compound together with its closest aqueous environment on the common brucinium corrugated layers. Performing racemic resolution of model compounds and studying structural relations between succeeding crystalline fractions, we also point out factors responsible for the successful separation of <i>N</i>-(4-nitrobenzoyl)­alanine by fractional crystallization of brucinium diastereomeric salts

Why Is the Resolution of Certain Racemic Modifications Inefficient? Formation of Diastereomeric Double Salts of Brucinium

Fractional crystallization of diastereomeric salts remains the most frequently used method for a separation of racemic compounds, and yet it has been performed by trial and error. For a better understanding of the chiral discrimination mechanism that is useful for the rationalization of optical resolution and help in choosing the crucial experimental parameters, structural investigations of products of both successful and unsuccessful racemic resolution are important. The former and the latter typically involve diastereomeric salts precipitating fractionally and the formation of solid solutions of diastereomeric salts or diastereomeric double salts, respectively. In this contribution, a mechanism of recognition leading to formation of the diastereomeric double salts is proposed based on crystal structures of three brucinium double salts (bis­(brucinium) <i>N</i>-(3,5-dinitrobenzoyl)-dl-alaninate methanol 3-solvate, bis­(brucinium) <i>N</i>-(3,5-dinitrobenzoyl)-dl-alaninate 5.75-hydrate, and bis­(brucinium) <i>N</i>-(3,5-dinitrobenzoyl)-dl-serinate 0.10-hydrate) as well as of some relevant diastereomeric salts (containing the d- or l-enantiomer of the alanine or the serine derivative)