Total synthesis of 16-desmethylepothilone B, epothilone B10, epothilone F, and related side chain modified epothilone B analogues

The macrolactonization-based strategy for the total synthesis of epothilones has been streamlined and improved to a high level of efficiency and stereoselectivity. This strategy has been applied to the construction of vinyl iodide 19 which served as a common intermediate for the synthesis of a series of natural and designed epothilones including an epothilone B10 (3), epothilone F (5), 16-desmethylepothilone B (14), pyridine epothilones 57a-57g, dimeric epothilones 59 and 61, and benzenoid epothilones 63a-63g.     

Total synthesis of epothilone A

[reaction: see text]Epothilones A (1) and B (2) are potent antitumor natural products with a Taxol-like mechanism of action. A total synthesis of epothilone A (1) is reported, which utilized chiral silane-based bond construction methodology to introduce the key C-6 and C-7 stereocenters of fragment 4. The C-15 stereocenter of fragment 5 was established by a lipase-mediated kinetic resolution. The fragments were assembled with a Suzuki coupling reaction and an aldol condensation and cyclized with a Yamaguchi-type macrolactonization reaction.     

The synthesis of cis- and trans-1,2-dibromocyclopropane

A preparative route to cis- and trans-1,2-dibromocyclopropane ($\text{1}$) was developed via the Hunsdiecker reaction of silver cyclopropane-1,2-dicarboxylate ($\text{2}$). Cis- and trans-$\text{2}$ gave the same ratio of cis- and trans-$\text{1}$ (1:3.2). The mechanism of this reaction is briefly discussed.     

Total synthesis of epothilone D by sixfold ring cleavage of cyclopropanol intermediates

The ring-opening or ring fragmentation reactions of cyclopropanol intermediates are used in the total synthesis of epothilone D for the creation of trisubstituted double bonds, an ethyl ketone functionality, as well as for the protection of carboxylic and ester groups. Epothilone D is obtained in 1.6% overall yield (24 steps in the longest linear sequence) starting from (R)-methyl 2,3-O-isopropylideneglycerate. The key cyclopropanol intermediates are efficiently obtained by titanium(IV)-catalyzed reactions of readily available esters with Grignard reagents.     

Total Synthesis of cis- and trans-3-Hydroxy-D-proline and (+)-Detoxinine

The unnatural enantiomer of the amino acid detoxinine and both diastereomeric 3-hydroxy-D-prolines have been prepared from D-mannitol via the O-silylated hydroxyproline 12 as a common key intermediate.     

Total synthesis of topopyrones B and D

[reaction: see text] We describe a straightforward synthesis of topopyrones B and D, which are potent and selective inhibitors of topoisomerase I. The chemistry should be suitable for additional structure-activity relationship (SAR) work.     

Efficient synthesis of cis- and trans-3,4-dihydroxy-3,4-dihydromollugin

An efficient synthesis of naturally occurring compounds isolated from Pentas longiflora, cis-3,4-dihydroxy-3,4-dihydromollugin 2, and trans-3,4-dihydroxy-3,4-dihydromollugin 3 is described. The O-protected mollugins were dihydroxylated using OsO4 to achieve the corresponding cis-dihydroxy derivatives in excellent yield. The synthesis of trans-3,4-dihydroxy-3,4-dihydromollugin was achieved using Oxone in good yield. A mechanism for the formation of cis-3,4-dihydroxymollugin acetonide from the reaction of mollugin with Oxone is proposed.     

Stereoselective total synthesis of cis- and trans-3-hydroxypipecolic acid

[reaction: see text] 3-Hydroxypipecolic acid, a nonproteinogenic cyclic alpha-amino acid, is a common structural moiety found in a large number of natural and synthetic compounds of medicinal significance. Utilizing D-serine as a chiral template, the present research describes efficient and straightforward routes to cis- and trans-3-hydroxypipecolic acids in enantiopure form. The key steps in the syntheses involve chelation-controlled addition of a homoallyl Grignard reagent to a protected serinal derivative toward stereoselective formation of the corresponding syn-amino alcohol adduct 3. On the other hand, zinc borohydride-mediated chelation-controlled reduction of a serine-derived alpha-aminoketone precursor leads to the formation of the corresponding anti-amino alcohol adduct 4 with high stereoselectivity. Following an efficient sequence of reactions, the above amino alcohol derivatives were subsequently transformed to the corresponding cis- and trans- title compounds, respectively.     

Stereospecific synthesis of cis- and trans-4-amino-3-hydroxythiophanes

The reduction of 4-benzoylamino- and 4-carbethoxyamino-3-ketothiophanes proceeds stereospecifically to form only trans-4-benzoylamino- and trans-4-carbethoxyamino-3-hydroxythiophanes, respectively, from which trans-4-amino-3-hydroxythiophane is obtained by alkaline hydrolysis. It was established that acid hydrolysis of trans-4-carbethoxyamino-3-hydroxythiophane leads only to trans-4-amino-3-hydroxythiophane, while acid hydrolysis of trans-4-benzoylamino-3-hydroxythiophane is accompanied by inversion to form cis-4-amino-3-hydroxythiophane. Derivatives of the cis- and trans-isomeric pairs of 4-amino-3-hydroxythiophanes were synthesized.Translated from Khimiya Geterotsilicheskikh Soedinenii, No. 12, pp. 1609–1613, December, 1970.     

Total synthesis of norcembrenolide B and scabrolide D

An efficient stereoselective synthesis of norcembrenolide B (8) and scabrolide D (9) is reported. The strategy is inspired by biogenetic relationships of related cembrenoids. Central to this approach is the construction of norbipinnatin J which upon selective C2 deoxygenation and C8 oxygenation produces norrubifolide and norcoralloidolide A. A sequence of site-selective oxidations and skeletal reorganizations then yields, in a divergent manner, compounds 8 and 9. The studies allow revision of the proposed structure of scabrolide D (9), which is identical to norcembrenolide C.     

Total asymmetric synthesis of sperabillins B and D

A concise route to the core fragment of sperabillins B and D, methyl (3R,5R,6R)-3,6-diamino-5-hydroxyheptanoate, has been developed with a subsequent novel protection strategy allowing the total asymmetric synthesis of sperabillins B and D.     

Stereodivergent synthesis of enantiopure cis- and trans-3-Ethyl-4-piperidineacetates

[reaction: see text] Starting from a common chiral bicyclic lactam 11, enantiopure trans- or cis-3-ethyl-4-piperidineacetate derivatives are obtained by conjugate addition of an enolate or a cuprate to the unsaturated lactams 12 or 18, respectively.     

Efficient stereoselective synthesis of enantiopure cis- and trans-1,2,4-trisubstituted piperidines

Enantiomerically pure (2R,4S)- and (2R,4R)-2-[(S)-1,2-dibenzyloxyethyl]-4-[2-(diphenylmethoxy)ethyl]-1-[(S)-1-phenylethyl]piperidines cis-1 and trans-1 have been synthesised from N-[(S)-1-phenylethyl]-(S)-2,3-di-O-benzylglyceraldimine in six steps in 31% and 18% overall yields, respectively. The efficiency of the synthetic strategy developed for the synthesis of these compounds relies on: (a) the totally diastereoselective tandem Mannich–Michael reaction between Danishefsky’s diene and the starting glyceraldimine, (b) the high yielding Wadsworth–Emmons reaction of the 4-piperidone intermediate and (c) the diastereodivergent reduction of the exocyclic C–C double bond at C₄ of the piperidine ring. These transformations led to 1,2,4-trisubstituted piperidines with two new stereogenic centres with excellent stereoselectivity.     

Enantioselective total synthesis of cis-(+)- and trans-(+)-disparlure

An expedient enantioselective synthetic approach for the gypsy moth sex-attractant pheromone cis-(+)-1 and trans-(+)-disparlure 2 is described employing the optimized combination of organocatalytic MacMillan’s self aldol reaction, Wittig olefination, regioselective ring opening of an epoxide and Mitsunobu esterification reactions as key steps.     

Total synthesis of epothilone a through stereospecific epoxidation of the p-methoxybenzyl ether of epothilone C

The total synthesis of epothilone A is described by the coupling four segments 4-7 a. Three of the segments, 4, 5 and 7 a, have only one chiral center; all other chiral centers were introduced by simple asymmetric catalytic reactions. The key steps are the ring opening of epoxide 5 with acetylide 8 for the construction of the C12-C13 cis double bond and a practical hydrolytic kinetic resolution (HKR) developed by Jacobsen group for the introduction the chiral center at C3. Especially, the stereospecific epoxidation of 3-O-PMB epothilone C 3 b through long-range effect of 3-O-PMB protecting group gave high yields of the C12-C13 alpha-epoxide for the synthesis of target molecule.     

Total synthesis of lamellarins D, H, and R and ningalin B

A concise total synthesis of lamellarins D (7 steps), H (7 steps), and R (5 steps) and ningalin B (5 steps) is achieved starting from the corresponding aldehydes and amines. The synthesis features three oxidative reactions as key steps in a biomimetic manner, involving an AgOAc-mediated oxidative coupling reaction to construct the pyrrole core, a Pb(OAc)(4)-induced oxidative cyclization to form the lactone, and Kita's oxidation reaction to form the pyrrole-arene C-C bond.