Reaction of (+)-usninic acid and several of its derivatives with diazomethane

New derivatives of (+)-usninic acid including products of ring expansion, methylation of enol and phenol hydroxyls, and formation of an oxirane ring in addition to products with pyran and furan rings annelated to ring A of (+)-usninic acid were prepared by reaction of (+)-usninic acid and its pyrazole derivatives with diazomethane.     

Synthesis of aurones based on usninic acid

(+)-Usninic acid was brominated at the acetyl group located on the aromatic ring. Aurones were synthesized based on the intramolecular cyclization of monobrominated (+)-usninic acid.     

An enantiospecific synthesis of (+)-hydroxy-exo-brevicomin

A concise enantiospecific synthesis of the pine beetle pheromone (+)-hydroxy-exo-brevicomin was achieved from l-(+)-tartaric acid in high yield. The key step involves the reduction of a keto-Weinreb amide derived from tartaric acid.     

Synthesis,chiroptical properties and absolute configuration of α-phenylglycidic acid

The (+)- and (-) enantiomers of potassium α-phenylglycidate, an irreversible inhibitor of the enzyme mandelate racemase, were synthesized by resolution of the diastereomeric esters with R-(-)-2-octanol. Base-catalyzed ring-opening of the resolved α-phenylglycidate esters gave the enantiomers of 2,3-dihydroxy-2-phenylpropanoic acid, also obtained by resolution of the racemic dihydroxy acid using ephedrine. A comparison of the chiroptical properties of the esters of α-phenylglycidic and 2,3-dihydroxy-2-phenylpropanoic acids with those of the structurally similar atrolactic and mandelic acids and their 2-methoxy-derivatives showed that the (-)-methyl 2,3-dihydroxy-2-phenylpropanoate corresponding to the (+)-enantiomer of potassium α-phenylglycidate, as well as the esters of α-phenylglycidic acid derived from the same (+)-potassium salt, were all configurationally related to S-(+)-atrolactic and mandelic acids. The configurational assignments made on the basis of the chiroptical data were confirmed by lithium aluminum hydride reduction of the (-)-2-octyl S- and R-α-phenylglycidates, which led exclusively to the R-(-)- and S-(+)-2-phenyl-1, 2-propanediols, respectively, previously related configurationally to R-(-)- and S-(+)-atrolactic acids.     

Formal total synthesis of (+)-didemniserinolipid B

The formal total synthesis of (+)-didemniserinolipid B, a marine tunicate possessing a 6,8-dioxabicyclo[3.2.1]octane framework, was accomplished starting from l-(+)-tartaric acid. The key transformations in the synthesis include the elaboration of a γ-hydroxy-amide readily obtained by desymmetrization of tartaric acid bis-amide via the controlled addition of a Grignard reagent followed by stereoselective reduction of the resulting ketone.     

Total synthesis of (+)-pederin. 2. Stereocontrolled synthesis of (+)-benzoylselenopederic acid and total synthesis of (+)-pederin

(+)-Benzoylselenopederic acid (1), a left half of (+)-pederin (3), was synthesized stereoselectively based on the Zn(BH₄)₂ reduction and total synthesis of (+)-pederin (3) was accomplished from 1 and the previously synthesized 2.     

Asymmetric synthesis of (+)-L-733, 060 and (+)-CP-99, 994 based on a new chiral 3-piperidinol synthon

[reaction: see text] Selective and potent neurokinin substance P receptor antagonists (+)-L-733, 060 (1) and (+)-CP-99, 994 (2) have been synthesized starting from a new (3S)-piperidinol synthon derived from l-glutamic acid. The methods featured a C-2 regioselective reduction of glutarimide (9), Lewis acid-promoted Si to C-2 phenyl group migration of 10, and stereoselective reduction of acetylated oxime 19 as the key steps.     

A Novel Asymmetric Synthesis of S-(+)-2-Amino-4-Phosphonobutanoic Acid

A novel asymmetric synthetic route to S(+)-2-amino -4-pbosphonobutanoic acid through the cyclic condensation of ethyl-4-diethoxyphosphonyl-2-oxo-butanoate with L-erythro-(+)-1, 2-diphenyl-2-hydrozyethylamine, followed by reduction and hydrolysis is described.     

Enantioselective synthesis of α-benzyloxy-ω-alkenals: application to the synthesis of (+)-exo-brevicomin, (+)-iso-exo-brevicomin,and (−)-isolaurepan

The enantioselective synthesis of α-benzyloxy aldehydes containing a terminal alkene was carried out from chiral pool l-(+)-tartaric acid by employing the stereoselective reduction of a 1,4-diketone as the key step. The synthetic utility of these aldehydes was demonstrated in the synthesis of pine beetle pheromones (+)-exo-brevicomin, (+)-iso-exo-brevicomin and a formal synthesis of 2,7-cis-disubstituted oxepane (−)-isolaurepan.     

Chemoenzymatic synthesis of phosphocarnitine enantiomers

Racemic phosphocarnitine 3 has been synthesized starting from diethyl 3-chloro-2-oxopropanephosphonate 4 in three steps involving reduction of 4 to the corresponding 2-hydroxyphosphonate 5, conversion of the latter to phosphonic acid 6, and final reaction with trimethylamine, affording the trimethylammonium salt of 3. Baker's yeast reduction of 4 and enzymatic kinetic resolution of (+/-)-5 afforded the enantiomerically pure precursors of phosphocarnitine, (R)-(+)-5 and (S)-(-)-5, which were converted to (S)-(-)- and (R)-(+)-phosphocarnitine 3, respectively.     

Synthetic studies on (+)-aplasmomycin. 1. Stereoselective synthesis of the C-12˜C-17 segment

The C-12˜C-17 segment of (+)-aplasmomycin ( ) was synthesized stereoselectively starting from (−)-malic acid based on the stereoselective ketone reduction.     

Asymmetric synthesis of unsaturated α-benzyloxyaldehydes: an enantioselective synthesis of (+)-exo-brevicomin

Enantioselective synthesis of α-hydroxy aldehydes with an alkene tether was accomplished from l-(+)-tartaric acid, employing stereoselective reduction of a 1,4-diketone with L-selectride as the key step. Synthetic utility of these aldehydes was demonstrated in the synthesis of pine beetle pheromone (+)-exo-brevicomin.     

Synthesis of anti-HIV lithospermic acid by two diverse strategies

An efficient and convergent route for the synthesis of the natural product (+)-lithospermic acid, which possesses anti-HIV activity, was accomplished. The (±)-trans-dihydrobenzo[b]furan core therein was prepared by two different strategies. The first strategy involved the use of a palladium-catalyzed annulation to generate an appropriately substituted benzo[b]furan ester followed by a stereoselective reduction of a carbon-carbon double bond with Mg-HgCl(2)-MeOH. The second strategy relied on an aldol condensation between a suitably substituted methyl arylacetate and 3,4-dimethoxybenzaldehyde, followed by cyclization. Finally, a total synthesis of (+)-lithospermic acid was completed via coupling of a trans-dihydrobenzo[b]furan cinnamic acid with an enantiomerically pure methyl lactate.     

Significant enhancement of electron transfer reduction of NAD(+) analogues by complexation with scandium ion and the detection of the radical intermediate-scandium ion complex

4-Acetyl-N,N-diisopropyl-1-benzylnicotinamidinium ion (ABNA(+)) and 1-benzyl-4-phenylnicotinamidinium ion (PhBNA(+)) were newly synthesized as NAD(+) analogues to examine the electron-transfer reactivity and the effects of metal ions on the reactivity in comparison with those of 1-benzylnicotinamidinium ion (BNA(+)) and 1-methyl-4-phenylpyridinium ion (MPP(+)) which has no amide or acetyl group. A remarkable positive shift in the one-electron reduction potential of ABNA(+) was observed in the presence of Sc(3+) which forms a 1:1 complex with ABNA(+) through both acetyl and amide groups, whereas no such shift in the presence of Sc(3+) was observed for the one-electron reduction of MPP(+) which has no acetyl or amide group. Similar but less positive shifts in the one-electron reduction potentials were observed in the presence of Sc(3+) for the one-electron reduction of BNA(+) and PhBNA(+) both of which have only one amide group. The rate of electron-transfer reduction of ABNA(+) is enhanced significantly by the complexation with Sc(3+) to produce stable ABNA(*)-Sc(3+) complex which has been successfully detected by ESR. The electron self-exchange rates of the MPP(*)/MPP(+) system have been determined from the ESR line width variation and are compared with those of the ABNA(*)/ABNA(+) system.     

The first synthesis of (-)-asperpentyn and efficient syntheses of (+)-harveynone, (+)-epiepoformin and (-)-theobroxide

A generally applicable strategy for the synthesis of a range of polyoxygenated cyclohexane natural products has been developed. The enantioselective syntheses of (-)-theobroxide, a polyoxygenated cyclohexane natural compound with potent growth inducing properties in potato microtubers has been achieved via a 1,2 O-silyl migration between trans-hydroxyl groups and a remote hydroxyl directed epoxidation of an enone derived from quinic acid. A thus derived alpha-iodoenone was subjected to Stille coupling with tetramethylstannane to afford the first title compound. A similar strategy enabled a route to the complete asymmetric synthesis of the acetylenic phytotoxin (+)-harveynone. By selective reduction of (-)-theobroxide, (+)-epiepoformin was also prepared in enantiopure form and similarly, stereoselective reduction of (+)-harveynone completed the first enantioselective synthesis of (-)-asperpentyn, another natural compound with antimicrobial activity.     

Enantiospecific synthesis of (−)-2-hydroxy-exo-brevicomin

An enantiospecific synthesis of (−)-2-hydroxy-exo-brevicomin was achieved from l-(+)-tartaric acid in high yield. The key step involves a very highly diastereoselective reduction of a keto Weinreb amide.     

An improved synthesis of 10-isobornylsultone

A modified and improved synthesis of 10-isobornylsultone in three steps and in 81% overall yield starting from (+)-camphor-10-sulfonic acid is described. The synthesis proceeds via methyl sulfonate ester formation, stereoselective reduction and base-catalysed intramolecular cyclisation.     

γ- And δ-lycorane

Hydrogenation of -anhydrodihydrocaranine (V) or anhydrocaranine (VII) with Adams catalyst in acetic acid or the Hauptmann reduction of -dihydrocaranone (XX) yielded (—)γ-lycorane (XVII). Catalytic reduction of β-anhydrodihydrocaranine (IX) with palladium-carbon in ethanol gave (+)γ-lycorane (XVIII), while with Adams catalyst in acetic acid it afforded (+)δ-lycorane (XIX) along with (—)β-lycorane (III). Reduction of anhydrocaranine in ethanol gave (±)γ-lycorane which was also obtained by hydrogenation of anhydrolycorine (X). Based on these findings, the configurational structures of -, β-, γ- and δ-lycorane were established and the configuration of dihydrolycorine was confirmed.     

Stereoselective total synthesis of (+)-cardiobutanolide

Stereoselective synthesis of styryllactone (+)-cardiobutanolide was accomplished in good overall yield from d-(-)-tartaric acid. Key features of the synthesis include the elaboration of a gamma-hydroxy butyramide obtained from the dimethylamide of tartaric acid, involving a combination of the addition of 1,3-dithian-2-yllithium and stereoselective reduction.     

Enantiospecific synthesis of carbapentostatins

In this paper we describe enantioselective syntheses of (+)-carbapentostatin (8) and its cyclopentyl analogue 12b. A new and efficient one-pot, two-step preparation of aldehyde 15 has been developed, based on the borane reduction of N-Pf-protected L-aspartic acid gamma-methyl ester (13) and Swern oxidation of the resulting alcohol. Homologation to diester 18 and ring formation by Dieckman cyclization, followed by reduction and dehydration steps, afford the 4-amino-1-cyclopentenemethanol derivative 22. Hydroboration and oxidation transform this compound stereospecifically into aminocyclopentanol 26, the key aminocyclitol component for an asymmetric synthesis of (+)-carbapentostatin.