The C4 hydroxyl group of phorbol esters is not necessary for protein kinase C binding

A new tigliane-type diterpenoid from Euphorbia tirucalli

Five tigliane (1-5) and one ingenane (6) diterpenoids were isolated from the ethanol extract of Euphorbia tirucalli. The structures of these compounds were identified based on analysis of their spectroscopic data. Among them, compound 12-O-(2E,4E,6E,8E-tetradecatetraenoyl)-13-O-isobutyroyl-4β-deoxyphorbol (1) was a new tigliane. The Rho123 effluxion assay showed that tiglianes with a trans-fused 5/7 ring system such as compounds 1, 2, and 4 had potent inhibitory activity against P-glycoprotein in HepG2/ADR cells.

Reactivation of latent HIV-1 in vitro using an ethanolic extract from Euphorbia umbellata (Euphorbiaceae) latex

Euphorbia umbellata (E. umbellata) belongs to Euphorbiaceae family, popularly known as Janauba, and its latex contains a combination of phorbol esters with biological activities described to different cellular protein kinase C (PKC) isoforms. Here, we identified deoxi-phorbol esters present in E. umbellata latex alcoholic extract that are able to increase HIV transcription and reactivate virus from latency models. This activity is probably mediated by NF-kB activation followed by nuclear translocation and binding to the HIV LTR promoter. In addition, E. umbellata latex extract induced the production of pro inflammatory cytokines in vitro in human PBMC cultures. This latex extract also activates latent virus in human PBMCs isolated from HIV positive patients as well as latent SIV in non-human primate primary CD4+ T lymphocytes. Together, these results indicate that the phorbol esters present in E. umbellata latex are promising candidate compounds for future clinical trials for shock and kill therapies to promote HIV cure and eradication.

Synthesis and biological evaluation of 12-aminoacylphorboids

Spurred by the paradoxical anti-inflammatory activity of some aminoacylphorbol derivatives, the naturally occurring and epimeric N,N-dimethylvalinoyl-4alpha-4-deoxyphorbol derivatives 3b and 3d have been prepared from 4alpha-4-deoxyphorbol (3e), a byproduct of the isolation of phorbol from Croton oil and a phorboid polyol so far largely overlooked in terms of biological activity. The configuration of the side chain stereocenter was confirmed for both natural products, and to investigate the side chain structure-activity relationships within this class of compounds, their corresponding N,N-dimethylglycinate (3g) and nor (3h) and di-nor derivatives (3i, 3j) were also prepared. By using a PKC-sensitive model of HIV-1 latency (activation of HIV- gene expression in Jurkat-LAT-GFP cells), it was found that both 3b and 3d can activate PKC-dependent responses, while a series of experiments with isoform-specific PKC inhibitors showed that these compounds target PKCalpha and -delta. Both N,N-dimethylation and the presence of side chain alpha-substitution were critical for activity. Selective PKC binding, rather than COX inhibition, might explain the paradoxical anti-inflammatory activity of extracts containing aminoacylphorboids in the mouse ear edema assay.

Diterpene esters and phenolic compounds from Sapium insigne (ROYLE) BENTH. ex HOOK. fil

From the leaves of Sapium insigne (ROYLE) BENTH. ex HOOK. fil., two new phorbol derivatives, such as 16-hydroxyphorbol-16-acetate (4) and 4beta-deoxy-16-hydroxyphorbol-16-acetate (5) along with twelve known phenolic compounds such as 3-O-caffeoyl quinic acid (1), 1-O-galloyl-beta-D-glucose (2), 1,3-di-O-galloyl-beta-D-glucose (3), rutin (6), 1,3,4,6-tetra-O-galloyl-beta-D-glucose (7), quercetin (8), guaijaverin (9), nicotiflorin (10), scopolin (11), methyl gallate (12), corilagin (13) and 1,3,6-tri-O-galloyl-beta-D-glucose (14) were isolated. All of these compounds have been isolated for the first time from this plant.

Identification of potent, selective protein kinase C inhibitors based on a phorbol skeleton

The elucidation of specific functions of protein kinase C (PKC) subtypes in physiological processes is an important challenge for the future development of new drug targets. Subtype-selective PKC agonists and antagonists are useful biological tools for this purpose. Most of the currently used PKC modulators elicit their activities through binding to the ATP binding site of PKC, which shares many features with other kinases. PKC modulators that target the PKC regulatory domain are considered to be advantageous in terms of selectivity, because the structure of the regulatory domain is intrinsic to each PKC subtype. In this paper, we describe the identification of new potent and conventional PKC-selective inhibitors that target the regulatory domain. The inhibitors contain a phorbol skeleton, a naturally occurring potent and selective PKC regulatory domain binder, with a perfluorinated alkyl group and a polyether hydrophilic chain on a terephthaloyl aromatic ring at the C12 position. Both of these substituents are essential for the potent inhibitory activity. Specifically, the binding affinity between PKC and the phorbol ester analogues was improved by an electron-deficient aromatic ring at C12. This finding cannot be explained by the previously proposed binding model and suggests a new binding mode between phorbol esters and PKC.

Design, synthesis, and structure–activity relationship of new isobenzofuranone ligands of protein kinase C

Protein kinase C (PKC) is a family of enzymes, which play important roles in intracellular signal transduction. We have designed novel PKC ligands having an isobenzofuranone template, based on the proposed interaction of DAG (1,2-diacyl-sn-glycerol) with the PKCdelta C1B ligand-binding domain. Several isobenzofuranone derivatives were synthesized and their PKCalpha binding activities were evaluated. The pivaloyl derivative 1f was found to be a strong PKCalpha ligand, and the structure-activity relationship is well explained by our proposed binding model.