mezerein and resiniferatoxin

This review summarizes the efforts to develop a radical-mediated three-component reaction and its application to a convergent approach to synthesize the 5/7/6-tricyclic framework (ABC-rings) of the densely functionalized dephnane diterpene, resiniferatoxin. The α-alkoxy bridgehead radical species, which was designed as the radical donor of the three-component reaction, was generated from O,Se- and O,Te-acetals under two different conditions. The generated α-alkoxy bridgehead radical effectively underwent the three-component reaction with α,β-unsaturated ketones and allyltributyltin/aldehyde under each of the conditions, giving rise to a wide variety of multiply functionalized 2,3-trans disubstituted cyclopentenone moieties. One of the established reactions was utilized as the key assembling reaction of the ABC-tricyclic framework of resiniferatoxin. The reaction of the bridgehead radical of the highly functionalized 6-membered C-ring, the 5-membered A-ring, and an allyltributyltin derivative effectively produced the C4-branched AC-rings. The last B-ring was constructed from the coupling adduct in two steps through the 7-endo cyclization, delivering the tricyclic framework possessing the correct C8 and 9-stereocenters of resiniferatoxin. The present methods demonstrate the power of the three-component reaction using an α-alkoxy bridgehead radical in a convergent approach to the complex architectures of daphnane diterpenes.

Topics: Chemistry Techniques, Synthetic; Diterpenes; Euphorbiaceae; Neurotoxins; TRPV Cation Channels

Tumor-promoting phorbol esters are potent inflammatory agents for mouse skin, and the potential mechanistic role of inflammation in tumor promotion is under active investigation. We have shown previously that resiniferatoxin, a uniquely irritant phorbol-related diterpene, acts as a capsaicin analogue to induce and then to block neurogenic inflammation. We report here that pretreatment of CD-1 mice with resiniferatoxin blocked the early (3 h) erythema and edema (6 h) in response to phorbol 12-myristate 13-acetate (PMA), whereas the edema at later times (12-24 h) was only partially blocked. Since the efficiency of resiniferatoxin pretreatment decreased as a function of time if PMA was applied 24, 48, or 96 h after resiniferatoxin administration, the late edema response to PMA may be a combination of increasing edema of nonneurogenic origin and the recovering neurogenic response due to the decreasing desensitization. For other phorbol esters, 12-deoxyphorbol mono- and diesters, and mezerein, differing kinetics of edema and differing degrees of blockade of edema following resiniferatoxin pretreatment were observed, as expected from the discrepancies between their inflammatory and tumor-promoting activities. PMA-induced skin hyperplasia, unlike edema, was not inhibited by resiniferatoxin pretreatment, suggesting that the early component of neurogenic inflammation was not essential for hyperplasia under our conditions. Distinction between inflammatory mechanisms may help to clarify the role of inflammation in tumor promotion.

Topics: Administration, Topical; Animals; Diterpenes; Dose-Response Relationship, Drug; Erythema; Female; Hyperplasia; Inflammation; Mice; Mice, Inbred Strains; Phorbol Esters; Skin; Terpenes; Tetradecanoylphorbol Acetate

Topics: Animals; Diterpenes; Ear Diseases; Erythema; Humans; In Vitro Techniques; Mice; Platelet Aggregation