Phorbol diterpenes

Materials. I-EGF was either made by iodinating mouse EGF (Biomedical Technologies Inc.) by the chloramine T method, to a specific activity of approximately 1-2 Ci/ xmol, using Na- I (Amersham) or purchased from New England Nuclear. Phorbol diterpene esters were purchased from Sigma. Palytoxin was isolated from Palythoa tuberculosa as previously described (1). 

The Wender group has investigated the (5 + 2) cycloaddition for quite some time and made seminal contributions to this important reaction. The group has also made fundamental contributions to higher order cycloadditions, thus opening up possibilities for the synthesis of natural products containing medium-sized rings. The first example leads toward the phorbol diterpenes... 

Long-chain ester derivatives of phorbol, a tetracyclic diterpene from the seed oil of Croton tiglium L., including its most abundant representative, 12-0-tetradecanoylphorbol-13-acetate (65), are potent activators of protein kinase G (PKG) and are used as standard tumor promoters for the study of experimental carcinogenesis in animal models." ... 

Several studies have examined the chemistry of Euphorbia species. A majority of these investigations have focused on the chemical character of the plant latex relative to taxonomy (, ) or mammalian toxicity Toxic Ingenane diterpenes (phorbols) have also been... 

Several effects of forskolin on B-lymphocytes, the cells of the immune system responsible for the production of immunoglobulins, have further been reported. This diterpene was found to inhibit cellular proliferation of B cells stimulated either by antibodies to surface immunoglobulins (anti-mu), and an antibody to CD20 antigen or 12-O-tetradecanoyl phorbol 13-acetate [219]. There was also a clear inhibition of G1 entry and DNA synthesis, and forskolin maintained its inhibitory effect even when added later after anti-mu stimulation. Additionally, no differences were found in the inhibitory effect of forskolin on neoplastic B cells, as compared to the responses of normal cells. Growth inhibition associated with an accumulation of cells in G1 was later found when cells of the B-lymphoid precursor cell line Reh were incubated with forskolin [220]. In that study, a delay of cells in G2/M prior to G1 arrest was observed, suggesting that important restriction points located in the G1 and G2 phases of the cell cycle may be controlled by forskolin (due to cAMP levels elevation). In a subsequent study [221], it was found that the arrest of Reh cells was accompanied by rapid dephosphorylation of retinoblastoma protein, which was suggested to be a prerequisite for the forskolin mediated arrest of these cells in Gl. 

The phorbol 33 is a tigliane diterpene whose 12, 13-diesters play a principal role in efforts to understand biological activities such as carcinogenesis and... 

Tigliane (G5 C7 C61 C3) diterpenes include the highly irritant, toxic, co-carcinogenic, PKC activating phorbol esters from Euphorbiaceae plants. While not being activated by the parent compound phorbol, PKC is activated by plant-derived esters of phorbol, 4-deoxyphor-bol and 12-deoxyphorbol (e.g. 12-0-palmitoyl-16-hydroxy-phorbol 13-acetate, 12-deoxyphorbol 13-benzoate, 12-deoxyphorbol 13-phenylacetate, 12-deoxyphorbol 13-phenylacetate-20-acetate, sapintoxin A (4-deoxyphorbol 12-(2-methylamino)benzoate-l3-acetate) and 12-tetradecanoylphorbol 13-acetate (TPA)), as well as by synthetic phorbol esters. 

Deoxyphorbol 13-phenylacetate (phorbol ester tigliane diterpene)... 

Polyterpenes, diterpenes (phorbol esters), lipophilic flavonoids, quinones... 

Another important use of pure natural substances is as pharmacological or biochemical tools for the study of novel mechanisms of action, or of pathophysiological processes e.g. forskolin is a diterpene in the root of Coleus forskohlii (Lamiaceae), which activates adenylate cyclase and causes an increase in cellular c AMP levels. Phorbol esters (from family Euphorbiaceae) stimulate protein kinase C, and tetrodotoxin in Fu iuspc-cies influences the transport of sodium ions. 

Pborbol and Its Relatives.— The Euphorbiaceae are a rich source of diterpenes. The hydrocarbon casbene (126), which is clearly related to the macrocyclic diterpene cembrene, has been isolated from Ricinus communis It may also be related to the parent hydrocarbon of the phorbol group of diterpenoids. 

Plants of the Euphorbiaceae family and particularly members of the Euphorbia genus have long been known to yield latexes with irritant and carcinogenic properties and these properties have been associated with diter-penes of the phorbol class. Members of the Euphorbia genus also contain diterpenes with other skeletons, among them the ingenane derivative PEP005 (38). " ... 

A dereplication example that illustrates the use of microscale derivatization and analysis by GC-MS is an identification of a series of bioactive diterpenes by NCI researchers (35). The extract from Croton cuneatus showed activity in a phorbol dibutyrate receptor, binding assay, and, on analysis, could be separated by HPLC into a group of seven very minor, related components. Following hydrolysis and acetylation, all seven components appeared to give rise to only two peaks, which by GC-CIMS analysis were judged to be phorbol tetraacetates. It was concluded that the seven compounds were probably van-ous esters of 4a-, or 16-hydroxylated phorbol analogs (Fig. 6). 

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