24 research outputs found
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<sup>+</sup>···O<sup>–</sup> 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)