Concise synthesis of the plant growth regulator theobroxide

Recent progress in the synthesis of the furanosteroid family of natural products

This review focuses on an overview of recent advances in the synthesis of furanosteroids and illustrates their applications in medicinal chemistry over the period of 2005–present.

Chemoenzymatic synthesis of (2R,3R,4R)-dehydroxymethylepoxyquinomicin (DHMEQ), a new activator of antioxidant transcription factor Nrf2

Dehydroxymethylepoxyquinomicin (DHMEQ, 1a) is a specific and potent inhibitor of NF-κB, and it is now being developed as an anti-inflammatory and anticancer agent. While previously only the (2S,3S,4S)-form had been available from the racemate by using lipase-catalyzed enantioselective resolution, in the present study a new route for production of the (2R,3R,4R)-form was established by use of a chemoenzymatic approach. (1R*,2R*,3R*)-2,3-Epoxy-5-N-[(2-hydroxybenzoyl)amino]-4,4-dimethoxycyclohex-5-en-1-ol (2a) was hexanoylated on both secondary and phenolic hydroxy groups, and subjected to Burkholderia cepacia lipase-catalyzed hydrolysis. The reaction proceeded in a highly enantioselective manner (E >500) to give (1S,2S,3S)-2a in an enantiomerically pure state. Several chemical steps of transformation from the enzyme reaction product gave (2R,3R,4R)-DHMEQ (1a) without any loss of stereochemical purity. Moreover, we newly found that (2R,3R,4R)-DHMEQ activated Nrf2, which is a transcription factor that induces the expression of multiple antioxidant enzymes. It activated Nrf2 in a promoter reporter assay. It also increased the expression of target antioxidant proteins and cancelled ROS-induced cell death in a neuronal cell line. Thus, (2R,3R,4R)-DHMEQ was efficiently prepared by a newly designed route using lipase, and it may be useful as a new anti-inflammatory agent.

Mode of action of epoxyphomalins A and B and characterization of related metabolites from the marine-derived fungus Paraconiothyrium sp

Epoxyphomalins A (1) and B (2) are highly potent cytotoxic fungal metabolites. During the course of purifying larger quantities of 1 and 2 from Paraconiothyrium sp. fermentation extracts, three new epoxyphomalins (3-5) were isolated and characterized, showing modifications to the oxidation pattern of the cyclohexene moiety or of C-9 of the decalin system. IC(50) values for cytotoxicity against a panel of 36 human tumor cell lines were determined for all new compounds. Compound 4 was found to be cytotoxic particularly toward prostate PC3M (IC(50) = 0.72 μM) and bladder BXF 1218 L (IC(50) = 1.43 μM) cancer cell lines. In addition, inhibition of chymotrypsin-, caspase-, and trypsin-like activity of purified 20S proteasomes was determined for epoxyphomalins A (1) and B (2). The results indicate that compounds 1 and 2 exert their cytotoxic effect through potent inhibition of the 20S proteasome.

Enantioselective Synthesis of Natural Polyoxygenated Cyclohexanes and Cyclohexenes from [(p-Tolylsulfinyl)methyl]-p-quinols

Exploitation of the beta-hydroxysulfoxide fragment present in a number of enantiomerically pure (SR)- and (SS)-[(p-tolylsulfinyl)methyl]-p-quinols allowed chemo- and stereocontrolled conjugate additions of different organoaluminium reagents to the cyclohexadienone moiety. The same fragment was also shown to act as an efficient chiral masking carbonyl group, after oxidation to sulfone and retroaddition in basic medium, with elimination of methyl p-tolyl sulfone. Through the use of both transformations as key steps, enantiocontrolled syntheses of different natural products-such as the two enantiomers of dihydroepiepoformin, (-)-gabosine O, (+)-epiepoformin, (-)-theobroxide and (+)-4-epigabosine A (an epimer of the natural product gabosine A)-has been achieved. The presence of the beta-hydroxy sulfone moiety makes the cyclic structures rigid, allowing a number of stereoselective transformations such as carbonyl reductions, enone epoxidations or cis-dihydroxylations, en route to the natural structures. The observed selectivities were dependent on the particular substitution in each substrate, providing evidence of a strong influence of remote groups on the preferred approach of the reactants to the reactive conformations. An advanced precursor of natural (+)-harveynone was also synthesized, but the isolation of the natural product was not possible because of the instability of the corresponding enone, containing a triple bond, under the basic conditions necessary to eliminate the beta-hydroxy sulfone. This demonstrated that the limitations of the use of the beta-hydroxy sulfoxide as a chiral protecting carbonyl group were dependent on the relative stabilities of the final targets in the presence of the required base.