Synthesis of a tritiated 3-dehydroecdysteroid putative precursor of ecdysteroid biosynthesis

First synthesis of ent-desmosterol and its conversion to ent-deuterocholesterol

We report the first synthesis of the unnatural enantiomer of desmosterol (ent-desmosterol). The sterol nucleus was constructed enantiospecifically, followed by stepwise addition of the side chain. Beginning with ent-androst-4-ene-3,17-dione, ent-desmosterol was synthesized in 13 steps and 20% yield. Protected ent-desmosterol was subjected to catalytic deuteration to afford ent-deuterocholesterol. Ent-desmosterol and ent-deuterocholesterol will be used to study the importance of sterol absolute configuration for sterol-lipid interactions in biophysical studies and in biological systems.

Synthesis and antiviral activity of 4-benzyl pyridinone derivatives as potent and selective non-nucleoside human immunodeficiency virus type 1 reverse transcriptase inhibitors

Several 4-benzyl analogues of 5-ethyl-6-methyl-4-(phenylthio)pyridin-2(1H)-ones were synthesized and evaluated for their anti-HIV-l activities. Key transformations include metalation at the 4-C-position of 5-ethyl-2-methoxy-6-methyl-3-pivaloylaminopyridine (5) and its coupling with benzyl bromide or benzaldehyde derivatives. Biological studies revealed that some of the new 4-benzylpyridinones show potent HIV-1 specific reverse transcriptase inhibitory properties. Compounds 14, 19, and 27, which inhibit the replication of HIV-1 in CEM-SS cells, with IC(50) values ranging from 0.2 to 6 nM are the most active compounds in this series. Biochemical studies showed that compound 27 strongly inhibited the activity of a recombinant HIV-1 RT. Moreover, the infectivity of isolated HIV-1 particles was severely decreased after exposure to compound 27. Although cross resistance is frequently observed between non-nucleoside reverse transcriptase inhibitors, compound 27 was capable of inhibiting a virus resistant to nevirapine with an IC(50) of 40 nM.

Stereospecific, mechanism-based, suicide inhibition of a cytochrome P450 involved in ecdysteroid biosynthesis in the prothoracic glands of Manduca sexta

The first required step in ecdysteroid (molting hormone) biosynthesis, dietary cholesterol (C) conversion to 7-dehydrocholesterol (7dC) via 7,8-dehydrogenation, is mediated by a microsomal cytochrome-P450 monooxygenase specific to the larval prothoracic gland. A subsequent series of unknown "black-box" oxidations of 7dC result in the unusual ring geometry (cis-A/B) and functionality (6-keto-7-ene-14-alpha-ol) of the ecdysteroids and has been thought to involve the initial formation of alpha-5,6-epoxy-7-dehydrocholesterol (alpha epo7dC). Pharmacological studies indicated that conversion of C to 7dC in prothoracic gland homogenates was strongly and equally inhibited by the isomeric cholesterol substrate analogues alpha- and beta-5,6-epoxycholesterol (alpha- and beta epoC) and alpha- and beta-5,6-iminocholesterol (alpha- and beta iminoC). With respect to the conversion of C to ecdysteroids by disrupted glands, however, the two alpha-isomeric substrates were 10-fold more inhibitory than were their beta-analogues. Indeed, alpha amino C was as active as the non-specific pyrimidyl cytochrome-P450 monooxygenase inhibitor fenarimol that shows moderate toxicity in many insect species. All four cholesterol analogues competitively inhibited cholesterol 7,8-dehydrogenation, but only alpha epoC and possibly alpha iminoC were desaturated to delta 7-products. Although the KmS (and KiS) for all the substrates were similar (1.7-6.0 x 10(-5) M), the Vmax for alpha epoC dehydrogenation was eight-fold higher than that of C, making it a superior substrate for following this reaction in ecdysteroidogenic tissues rich in endogenous C. The 7,8-dehydrogenation of alpha epoC and alpha iminoC by prothoracic glands would produce the potentially reactive intermediates, alpha epo7dC and alpha imino7dC, respectively. They, in turn, could then undergo facile, acid-catalyzed ring-opening to the allylic-stabilized carbo-cation electrophiles. These very reactive, transient species, if formed in the active site of the monooxygenase, would then alkylate either the heme group or the apoprotein of the cytochrome or both, leading to the irreversible inhibition of the enzyme. The present data show that alpha epoC and probably alpha iminoC are mechanism-based suicide inhibitors of the enzyme catalyzing cholesterol 7,8-dehydrogenation and may be the prototypes of a new class of selective insect control agents.