Synthesis of 7,8-disubstituted benzolactam-V8 and its binding to protein kinase C

Selective nitrogen insertion into aryl alkanes

Molecular structure-editing through nitrogen insertion offers more efficient and ingenious pathways for the synthesis of nitrogen-containing compounds, which could benefit the development of synthetic chemistry, pharmaceutical research, and materials science. Substituted amines, especially nitrogen-containing alkyl heterocyclic compounds, are widely found in nature products and drugs. Generally, accessing these compounds requires multiple steps, which could result in low efficiency. In this work, a molecular editing strategy is used to realize the synthesis of nitrogen-containing compounds using aryl alkanes as starting materials. Using derivatives of O-tosylhydroxylamine as the nitrogen source, this method enables precise nitrogen insertion into the Csp2-Csp3 bond of aryl alkanes. Notably, further synthetic applications demonstrate that this method could be used to prepare bioactive molecules with good efficiency and modify the molecular skeleton of drugs. Furthermore, a plausible reaction mechanism involving the transformation of carbocation and imine intermediates has been proposed based on the results of control experiments.

PKC in Regenerative Therapy: New Insights for Old Targets

Effective therapies for chronic or non-healing wounds are still lacking. These tissue insults often result in severe clinical complications (i.e., infections and/or amputation) and sometimes lead to patient death. Accordingly, several research groups have focused their efforts in finding innovative and powerful therapeutic strategies to overcome these issues. On the basis of these considerations, the comprehension of the molecular cascades behind these pathological conditions could allow the identification of molecules against chronic wounds. In this context, the regulation of the Protein Kinase C (PKC) cascade has gained relevance in the prevention and/or reparation of tissue damages. This class of phosphorylating enzymes has already been considered for different physiological and pathological pathways and modulation of such enzymes may be useful in reparative processes. Herein, the recent developments in this field will be disclosed, highlighting the pivotal role of PKC α and δ in regenerative medicine. Moreover, an overview of well-established PKC ligands, acting via the modulation of these isoenzymes, will be deeply investigated. This study is aimed at re-evaluating widely known PKC modulators, currently utilized for treating other diseases, as fruitful molecules in wound-healing.

Identification of a small molecule activator of novel PKCs for promoting glucose-dependent insulin secretion

Using an image-based screen for small molecules that can affect Golgi morphology, we identify a small molecule, Sioc145, which can enlarge the Golgi compartments and promote protein secretion. More importantly, Sioc145 potentiates insulin secretion in a glucose-dependent manner. We show that Sioc145 selectively activates novel protein kinase Cs (nPKCs; δ and ɛ) but not conventional PKCs (cPKCs; α, βI and βII) in INS-1E insulinoma cells. In contrast, PMA, a non-selective activator of cPKCs and nPKCs, promotes insulin secretion independent of glucose concentrations. Furthermore, we demonstrate that Sioc145 and PMA show differential abilities in depolarizing the cell membrane, and suggest that Sioc145 promotes insulin secretion in the amplifying pathway downstream of K(ATP) channels. In pancreatic islets, the treatment with Sioc145 enhances the second phase of insulin secretion. Increased insulin granules close to the plasma membrane are observed after Sioc145 treatment. Finally, the administration of Sioc145 to diabetic GK rats increases their serum insulin levels and improves glucose tolerance. Collectively, our studies identify Sioc145 as a novel glucose-dependent insulinotropic compound via selectively activating nPKCs.

Solventless lactam synthesis by intramolecular cyclizations of alpha-iminoester derivatives under microwave irradiation

We have previously reported a new synthesis of amides from esters and amines under microwave irradiation, offering much higher yields than those achieved with conventional heating [1]. We have now extended these studies to the ring closure of neat iminoesters I2, I3 and I4-I6 to give five- and six-membered ring lactams L5, L6 and larger lactams L7-L9 (where I means imine and L means lactam), respectively, under both classical heating conditions and microwave irradiation.

Synthesis and Pharmacological Evaluation of 8- and 9-Substituted Benzolactam-V8 Derivatives as Potent Ligands for Protein Kinase C, a Therapeutic Target for Alzheimer's Disease

A central element in the pathophysiology of Alzheimer's disease (AD) is the formation of amyloid plaques, which result from abnormal processing of the amyloid precursor protein (APP). The processing of APP is largely provided by three key enzymes, namely the alpha-, beta-, and gamma-secretases. As the latter two contribute to the formation of neurotoxic Abeta fragments while alpha-secretase does not, a decrease in the amyloidogenic products can be brought about either by inhibition of the beta- and gamma-secretases or through the activation of alpha-secretase. It is now known that the activation of protein kinase C (PKC) enhances alpha-secretase activity and therefore represents a possible target for the development of agents urgently needed for the treatment of this devastating neurodegenerative disorder. In the present study, new benzolactam-V8-based PKC activators were synthesized and tested for their binding affinity toward PKCalpha. All compounds tested showed binding values in the nanomolar concentration range. In accordance with previous publications, 9-substitution dramatically increased PKC binding affinity in comparison with the corresponding 8-substituted analogues. In addition to the location of the side chain on the aromatic ring, the binding affinities of these benzolactams were found to depend on the orientation, length, and electronic properties of this appendage. An interesting decrease in binding affinity was found for the 9-thienyl analogue 13, suggesting adverse electronic interactions of the sulfur atom with PKC or parts of the cellular membrane.

Toward the development of new medicinal leads with selectivity for protein kinase C isozymes

Tumor promoters such as phorbol esters bind strongly to protein kinase C (PKC) isozymes to induce their activation. Since each PKC isozyme is involved in diverse biological events in addition to tumor promotion, the isozymes serve as promising therapeutic targets. Tumor promoters bind to the C1A and/or C1B domain of conventional (alpha, betaI, betaII, and gamma) and novel PKC isozymes (delta, epsilon, eta, and theta). As these C1 domains play differential roles in PKC activation and their translocation in cells, the development of agents with binding selectivity for individual C1 domains is a pressing need. For this purpose, we established a synthetic C1 peptide library of all PKC isozymes. The library enabled us to identify indolactam-V (1) as a promising lead compound. Our diverse structure-activity studies on 1 indicated that the position of the hydrophobic substituent on the indole ring dominates the PKC isozyme- and C1 domain-selective binding rather than conformation of the nine-membered lactam. Moreover, we suggested that the indole ring of 1 could be involved in the CH/pi interaction with Pro-11 of the C1B domain of PKCdelta. This invaluable information will lead to the structural optimization of the PKCdelta ligand as exemplified by the design and synthesis of naphtholactam-V8 (21).

Synthesis of 7-substituted benzolactam-V8s and their selectivity for protein kinase C isozymes

[reaction: see text] Condensation of L-valine benzyl ester toluenesulfonic acid salt with a substituted cyclohexadione followed by aromatization with the assistance of NBS provides an N-aryl L-valine benzyl ester. This intermediate is converted into 7-substituted benzolactam-V8s using an asymmetric Strecker reaction as the key step. The target molecules show a different pattern of isozyme selectivity relative to the 8-substituted benzolactam-V8s.

Synthesis and modeling study of (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy- 8-(1-decynyl)-benzolactam-V8 as protein kinase C modulators

[structures: see text] Both (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy-8-(1-decynyl)benzolactam-V8 were designed and synthesized as PKC modulators. Biological assays reveal the (6R)-ligand to be 20-fold more potent than its (6S)-counterpart in binding to PKC alpha.