Reductive SN 2' Reaction of Epoxydienoate with Borane and its Application to the Synthesis and Structural Revision of an Antitumor Active Torrubiellutin Analogue.

A reductive SN 2' reaction of epoxydienoates and epoxyenoates with borane was developed to afford skipped dienoates and unconjugated enoates with trisubstituted Z-alkene linked to asymmetric centers on one side or both sides. This reaction was successfully applied to the alternative synthesis of an antitumor active artificial analogue of torrubiellutin C. A geometric isomer for α,ß-unsaturated amide of the artificial analogue was also synthesized. These syntheses clarified the true structure of the antitumor active artificial analogue of torrubiellutin C.

Total Synthesis of Sekothrixide Strategically Utilizing Regioselective Coupling of TMS-Protected Epoxy sec-Alcohol with Gilman Reagent.

A new efficient synthesis of sekothrixide was established on the basis of our developed regioselective coupling of epoxy sec-alcohol with Gilman reagent guided by a TMS group. The new synthetic route allowed an overall yield of 6.3% (26 steps) from optically active 3-silyloxy-2-methylaldehyde.

Syntheses of Polycyclic Tetrahydrofurans by Cascade Reactions Consisting of Five-Membered Ring Selective Prins Cyclization and Friedel-Crafts Cyclization.

A novel cascade reaction consisting of a five-membered ring selective Prins cyclization and a subsequent Friedel-Crafts cyclization is reported. Treatment of homocinnamyl alcohols and aromatic aldehydes with BF3·OEt2 in CH2Cl2 afforded hydrocyclopentafurans. Also hydrocyclopentafurans underwent the same cascade reaction after its furan ring cleavage upon treatment with BF3·OEt2 at room temperature. Various combinations of hydropentafurans and aromatic aldehydes or indole aldehydes permitted divergent synthesis of diquinane-furans stuck in aromatic rings.

Selective Mono-reduction of Pyrrole-2,5 and 2,4-Dicarboxylates.

Pyrrole-2,5-dicarboxylates were rapidly and selectively reduced to the corresponding mono-alcohol using 3 eq of diisobutylaluminum hydride at 0°C. Pyrrole-2,4-dicarboxylate showed the same reactivity; however, the selectivity decreased with pyrrole-3,4-dicarboxylate. When the nitrogen atom of the pyrrole-2,5-dicarboxylate is protected with a benzyl group, selective mono-reduction does not occur. Considering that furan-2,5-dicarboxylates did not give the corresponding mono-alcohol under the same conditions, the unprotected nitrogen atom of pyrrole apparently plays an important role in this selective mono-reduction.

Total synthesis and structural revision of sekothrixide.

The first total synthesis of 14-membered macrolide sekothrixide and the originally proposed structure are reported. Seven contiguous asymmetric centers in the side chain were constructed using ring-openings of several kinds of epoxide. Assembly of the left segment and right segment was performed on the basis of the RCM reaction to generate 14-membered lactones having an E-trisubstituted olefin. These synthetic results led to a revision of C4, C6, and C8 stereochemistry in the structure of natural sekothrixide.

Synthesis of 1-(4-aminobutyl)-2-iminoimidazolidin-4-one aimed at preparation of a creatinine-specific antibody.

For the purpose of obtaining a creatinine-specific antibody, a creatinine derivative with 4-aminobutyl, which was served as a linker for preparing the creatinine-bovine serum albumin (BSA) conjugate, was synthesized from 4-benzylaminobutan-1-ol in 8 steps. Production of anti-creatinine antibodies was observed in two rabbits using the creatinine-BSA conjugate, although their titer was rather low.

Synthesis and evaluation of a cyclopropane derivative of DHMEQ.

Dehydroxymethylepoxyquinomycin (DHMEQ, 1) is well known to inhibit nuclear factor-kappa B (NF-κB), which is closely associated with immune, inflammatory, and apoptotic processes as an inducible transcription factor. The inhibitory effect seems to be the result of the ring opening of an epoxide of 1 with Cys(38) of p65. We have synthesized an analog 4 containing a cyclopropanated quinol skeleton and examined its ability to inhibit NF-κB. Surprisingly, 4 showed no remarkable NF-κB inhibitory activity as determined through expression of cyclooxygenase-2 (COX-2) in an RAW264.7 macrophage cell line.

Synthetic studies of the lichen macrolide lepranthin. Stereoselective synthesis of the diolide framework based on regioselective epoxide-opening reactions.

Stereoselective synthesis of the 16-membered diolide 27, a fully functionalized congener of lepranthin (1), is described. The requisite five asymmetric carbon centers in monomer 23 were constructed in a highly stereoselective manner by using different epoxide-opening reactions of α,ß-unsaturated γ,δ-epoxy esters and epoxy alcohol derivatives as the key steps. The monomer 23 was successfully transformed into the MOM protected diolide 27 by Yamaguchi macrolactonization.

Stereoselective synthesis of the C(25)-C(36) segment of arenicolides A and B: determination of the configuration of the trisubstituted epoxide.

Two diastereomeric epoxides 4a and 4b corresponding to the C(25)-C(36) fragment of arenicolides A and B were synthesized in a stereoselective manner involving the Pd(0)-catalyzed stereospecific methoxy substitution reaction of epoxy unsaturated ester 6 with B(OMe)(3) as the key step. Comparison of the (1)H NMR spectra of the synthetic compounds with that of arenicolide A revealed that the configuration of the epoxide in arenicolides A and B is 30R and 31R.

Nitrile-promoted Rh-catalyzed intermolecular hydroacylation of olefins with salicylaldehyde.

Rh-catalyzed intermolecular hydroacylation between salicylaldehyde and alkenylnitriles proceeded at room temperature to preferentially give normal-hydroacylated products. Addition of CH3CN and NaOAc accelerated the Rh-catalyzed hydroacylation of monoolefins to exclusively produce the normal-hydroacylated products under mild reaction conditions. Plausible mechanisms for the regioselections are also described.

Double-chelation-assisted Rh-catalyzed intermolecular hydroacylation between salicylaldehydes and 1,4-penta- or 1,5-hexadienes.

Intermolecular hydroacylation between salicylaldehydes 1, 26-40 and 1,4-penta- or 1,5-hexadienes 4-13 by Rh-catalyst proceeded under mild reaction conditions to give a mixture of iso- and normal-hydroacylated products 14-25, 41-55, and 57-60. In the hydroacylation reaction, chelation of both salicylaldehyde and diene to the Rh-complex plays a crucial role. The ratio of iso- and normal-hydroacylated products could be regulated by the addition of salicylic acid or amines. The effects of various Rh-complexes, solvents, and additives were examined, and the plausible mechanisms of the catalytic cycle were proposed on the basis of the deuterium-labeling salicylaldehyde experiments.

Double-chelation-assisted Rh-catalyzed intermolecular hydroacylation.

[reaction: see text] Rh-Catalyzed intermolecular hydroacylation between salicylaldehydes and 1,5-hexadienes proceeded under remarkably mild reaction conditions to afford a mixture of iso- and normal-hydroacylated products in good yields. The experiments using deuterated salicylaldehyde-d revealed that "double chelation" of salicylaldehyde and 1,5-hexadiene to Rh-complex played vital roles in the catalytic cycle of intermolecular hydroacylation.

Intramolecular reaction of a phenonium ion. Novel lactonization of 4-aryl-5-tosyloxypentanoates and 4-aryl-5-tosyloxyhexanoates concomitant with a phenyl rearrangement.

The novel lactonizations of methyl 4-aryl-5-tosyloxypentanoate 1 and 4-aryl-5-tosyloxyhexanoate 3 concomitant with a phenyl rearrangement are reported. The lactonizations were promoted by silica gel or heating in various solvents. By examining the effects of substituents of the aromatic ring on the reactivity, it was found that the reaction proceeded via a phenonium ion. This finding was supported by the stereochemical results for the lactonization of optical active 1. Silica gel-promoted lactonization of 1 gave only gamma-lactone 2, whereas that of 3 afforded gamma-lactone 4 and delta-lactone 5. These lactonizations proved to be kinetically controlled. On the other hand, when 3c was heated in CH(3)NO(2) at 70 degrees C, the highly selective formation of 4c was observed. Further detailed experiments confirmed that the thermal lactonization in CH(3)NO(2) was thermodynamically controlled.