K-252c

K-252c is a cell-permeable, reversible, and ATP-competitive inhibitor of protein kinase C (PKC) and protein kinase A (PKA) with IC50 value of 2.45 μM and 25.7 μM, respectively. This component was inhibits β-lactamase, malate dehydrogenase and chymotrypsin with IC50 values of 8, 8 and 10 μM respectively [1].

Protein kinase is known as kinase enzymes that modify other proteins by chemically adding phosphate groups to them (phosphorylation). Phosphorylation can result in a functional change of the target protein (substrate) by changing enzyme activity, cellular location, or association with other proteins in the cells. PKA and PKC are important family member of AGC kinases.

K-252a was previously shown to block nerve growth factor (NGF)-induced neurite outgrowth and the changes in protein phosphorylation elicited by NGF in PC12h cells [2].

The effect of K-252c was also investigated on the severe combined immunodeficient (SCID) mouse-human skin model of psoriasis. It was shown that psoriasis significantly improved after 2 weeks treatment of K-252c [3].

References:
1.  Fabre S, Prudhomme M, Rapp M. Protein kinase C inhibitors; structure-activity relationships in K252c-related compounds. Bioorg Med Chem 1993,1:193-196.
2.  Hashimoto S. K-252a, a potent protein kinase inhibitor, blocks nerve growth factor-induced neurite outgrowth and changes in the phosphorylation of proteins in PC12h cells. J Cell Biol 1988,107:1531-1539.
3.  Raychaudhuri SP, Sanyal M, Weltman H, Kundu-Raychaudhuri S. K252a, a high-affinity nerve growth factor receptor blocker, improves psoriasis: an in vivo study using the severe combined immunodeficient mouse-human skin model. J Invest Dermatol 2004,122:812-819.

Synthesis of Pyrrolidin-2-ones and of Staurosporine Aglycon (K-252c) by Intermolecular Michael Reaction.[Pubmed:11674542]

J Org Chem. 1999 Jun 25;64(13):4697-4704.

Indolo[2,3-a]pyrrolo[3,4-c]carbazoles were isolated from nature, e.g., from low plants, especially fungi, as structurally rare natural substances. Responsible for naming and also the most important representative of this type is staurosporine (1), isolated from Streptomyces staurosporeus, and its aglycon (2), also known as staurosporinone or K-252c. 3,4-Disubstituted pyrrolidin-2-ones, a group of compounds with many interesting biological properties are related to staurosporinone. The most important property is the inhibition of protein kinase C (PKC), so that this antiproliferative agent can interfere with the cell cycle. The synthetic strategy, developed by us, allows the synthesis of pyrrolidin-2-ones by an intermolecular Michael addition, starting from nitroethene derivatives and substituted acetate Michael donors. With this method also enantioselective syntheses can be carried out using chiral auxiliaries. After reduction of the nitro group and subsequent lactamization, the lactam partial structure, which is essential for the biological activity, is obtained. Besides indole substituents, which were used for the synthesis of staurosporinone, substituted indole-, phenyl-, and pyridyl- as well as enantiomerically pure (S)-proline derivatives were used. Here, considerably high diastereoselectivity and enantioselectivity ((S)-pyrrolidine) could be detected. Just like the total synthesis of staurosporinone within three steps, the easiest and shortest approach reported up to now, with good to moderate yields, this sequence allows highly diastereoselective syntheses, which open the easy access to a new family of compounds.

Kinase inhibitors: not just for kinases anymore.[Pubmed:12672248]

J Med Chem. 2003 Apr 10;46(8):1478-83.

Kinase inhibitors are widely employed as biological reagents and as leads for drug design. Their use is often complicated by their lack of specificity. Although binding conserved ATP sites accounts for some of their nonspecificity, some compounds inhibit proteins not known to bind ATP. It has been found that promiscuous hits from high-throughput screening may act as aggregates. To explore whether this mechanism might explain the action of widely used nonspecific kinase inhibitors, 15 such compounds were studied. Eight of these, rottlerin, quercetin, K-252c, bisindolylmaleimide I, bisindolylmaleimide IX, U0126, indirubin, and indigo, inhibited three diverse non-kinase enzymes. Inhibition was time-dependent and sensitive to enzyme concentration; by light scattering, the compounds formed particles of 100-1000 nm diameter. These observations suggest that these eight kinase inhibitors, at least at micromolar concentrations, are promiscuous and act as aggregates. Results obtained from the use of these compounds at micromolar or higher concentrations against individual enzymes should be interpreted cautiously.

Indolocarbazoles exhibit strong antiviral activity against human cytomegalovirus and are potent inhibitors of the pUL97 protein kinase.[Pubmed:11080540]

Antiviral Res. 2000 Oct;48(1):49-60.

We have analyzed a panel of protein kinase inhibitors (PKIs) and found that some indolocarbazoles (Go6976, K252a, K252c) proved to be highly effective inhibitors of GCV-sensitive and -resistant human cytomegalovirus (HCMV) strains, but did not show any effect against herpes simplex virus. Antiviral activity was determined by focus reduction assays (IC(50) ranging from 0.009 to 0.4 microM). Other inhibitors of serine/threonine kinases (Go6850, H-7, roscovitine) were found to be ineffective. Virus yield at 5 days after infection was reduced by three orders of magnitude with nanomolar concentrations of the indolocarbazoles. These compounds were fully effective when added up to 24 h post infection and showed reduced activity up to 72 h post infection. Cytotoxicity assays in proliferating and non-proliferating cells demonstrated that the effective antiviral concentration of these compounds was significantly lower than either antiproliferative (IC(50)/CC(50) ranging from 6.5 to 390) or cytotoxic (IC(50)/CC(50) ranging from 72. 5 to 1000) doses. The effects of PKIs on the virus-encoded protein kinase pUL97 were studied using recombinant vaccinia viruses. Indolocarbazoles strongly inhibited both pUL97 autophosphorylation (IC(50) ranging from 0.0012 to 0.013 microM) and pUL97-dependent ganciclovir phosphorylation (IC(50) ranging from 0.05 to 0.26 microM). Other inhibitors of serine/threonine kinases showed only weak (Go6850) or no (H-7, roscovitine) effect on these pUL97 functions, while oxoflavone tyrosine kinase inhibitors had no effect at all.

Protein kinase C inhibitors; structure-activity relationships in K252c-related compounds.[Pubmed:8081852]

Bioorg Med Chem. 1993 Sep;1(3):193-6.

K252c-related compounds were synthesized with different framework flexibilities and different functions (imide, amide and amide-alcohol) on the non-indolic heterocycle. The inhibitory activities towards protein kinase C and protein kinase A are compared.

K-252c, a staurosporine analog isolated from Nocardiopsis sp., is a cell-permeable PKC inhibitor, with an IC50 of 2.45 µM. K-252c induces apoptosis in human chronic myelogenous leukemia cancer cells. K-252c also inhibits β-lactamase, chymotrypsin, and malate dehydrogenase.

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