Evaluation of a Novel Boron-Containing α-D-Mannopyranoside for BNCT.

Boron neutron capture therapy (BNCT) is a unique anticancer technology that has demonstrated its efficacy in numerous phase I/II clinical trials with boronophenylalanine (BPA) and sodium borocaptate (BSH) used as 10B delivery agents. However, continuous drug administration at high concentrations is needed to maintain sufficient 10B concentration within tumors. To address the issue of 10B accumulation and retention in tumor tissue, we developed MMT1242, a novel boron-containing α-d-mannopyranoside. We evaluated the uptake, intracellular distribution, and retention of MMT1242 in cultured cells and analyzed biodistribution, tumor-to-normal tissue ratio and toxicity in vivo. Fluorescence imaging using nitrobenzoxadiazole (NBD)-labeled MMT1242 and inductively coupled mass spectrometry (ICP-MS) were performed. The effectiveness of BNCT using MMT1242 was assessed in animal irradiation studies at the Kyoto University Research Reactor. MMT1242 showed a high uptake and broad intracellular distribution in vitro, longer tumor retention compared to BSH and BPA, and adequate tumor-to-normal tissue accumulation ratio and low toxicity in vivo. A neutron irradiation study with MMT1242 in a subcutaneous murine tumor model revealed a significant tumor inhibiting effect if injected 24 h before irradiation. We therefore report that 10B-MMT1242 is a candidate for further clinical BNCT studies.

Practical large-scale production of dihydrocapsiate, a nonpungent capsaicinoid-like substance.

Capsinoids represent a novel group of capsaicinoid-like substances found in a nonpungent cultivar, Capsicum annuum "CH-19 Sweet." They have capsaicinoid-like physiological and biological properties while lacking the harmful stimuli of capsaicinoids. A large-scale synthesis of dihydrocapsiate (DCT) is established in this work. 8-Methynonanoic acid (MNA) was synthesized by copper-catalyzed cross-coupling of ethyl 6-bromohexanoate with isobutylmagnesium bromide and subsequent hydrolysis. Lipase-catalyzed chemoselective esterification of vanillyl alcohol and MNA was performed at 50 °C under reduced pressure to remove water without solvents or drying agents. A slightly larger stoichiometric amount of MNA was used and the purification in the final stage was simplified to leave a small amount of MNA in the product, because we found that the presence of a small amount of MNA is necessary to stabilize DCT. DCT was synthesized according to the production, and stabilization methods described here has been filed as a new dietary ingredient.

Ammonium-directed olefinic epoxidation: kinetic and mechanistic insights.

The ammonium-directed olefinic epoxidations of a range of differentially N-substituted cyclic allylic and homoallylic amines (derived from cyclopentene, cyclohexene, and cycloheptene) have been investigated, and the reaction kinetics have been analyzed. The results of these studies suggest that both the ring size and the identity of the substituents on nitrogen are important in determining both the overall rate and the stereochemical outcome of the epoxidation reaction. In general, secondary amines or tertiary amines with nonsterically demanding substituents on nitrogen are superior to tertiary amines with sterically demanding substituents on nitrogen in their ability to promote the oxidation reaction. Furthermore, in all cases examined, the ability of the (in situ formed) ammonium substituent to direct the stereochemical course of the epoxidation reaction is either comparable or superior to that of the analogous hydroxyl substituent. Much slower rates of ring-opening of the intermediate epoxides are observed in cyclopentene-derived and cycloheptene-derived allylic amines as compared with their cyclohexene-derived allylic and homoallylic amine counterparts, allowing for isolation of these intermediates in both of the former cases.

One-pot conversions of olefins to cyclic carbonates and secondary allylic and homoallylic amines to cyclic carbamates.

Sequential treatment of a 1,2-disubstituted olefin with m-CPBA, Br3CCO2H, and DBU results in the one-pot, stereospecific conversion of the olefin to the corresponding disubstituted cyclic carbonate (1,3-dioxolan-2-one). The reaction proceeds via an initial epoxidation followed by S(N)2-type epoxide ring opening by Br3CCO2H and subsequent base-promoted carbonate formation upon elimination of bromoform. When a solution of a secondary allylic or homoallylic amine and Br3CCO2H is sequentially treated with m-CPBA then DBU, the product of the reaction is a cyclic carbamate (1,3-oxazolidin-2-one or 1,3-oxazinan-2-one).

Ammonium-directed oxidation of cyclic allylic and homoallylic amines.

The ammonium-directed olefinic oxidation of a range of cyclic allylic and homoallylic amines has been investigated. Functionalization of a range of allylic 3-(N,N-dibenzylamino)cycloalk-1-enes with m-CPBA in the presence of Cl(3)CCO(2)H gives exclusively the corresponding syn-epoxide for the 5-membered ring (>99:1 dr), the anti-epoxide for the 8-membered ring (>99:1 dr), and predominantly the anti-epoxide for the 7-membered ring (94:6 dr). Oxidation of the homoallylic amines 3-(N-benzylamino)methylcyclohex-1-ene and 3-(N,N-dibenzylamino)methylcyclohex-1-ene gave, in both cases, the corresponding N-protected 1,2-anti-2,3-syn-3-aminomethylcyclohexane-1,2-diol with high levels of diastereoselectivity (>or=90:10 dr). The versatile synthetic intermediates resulting from these oxidation reactions are readily transformed into a range of amino diols.

The chiral auxiliary N-1-(1'-naphthyl)ethyl-O-tert-butylhydroxylamine: a chiral Weinreb amide equivalent.

The chiral auxiliary N-1-(1'-naphthyl)ethyl-O-tert-butylhydroxylamine is readily prepared from N-hydroxyphthalimide in four steps, with resolution giving access to both enantiomers in > 98% ee, on a multigram (> 25 g) scale. Conversion to a range of N-acyl derivatives, followed by highly diastereoselective alkylation (> or = 94% de) gives the corresponding chiral, 2-substituted derivatives as single diastereoisomers (> 98% de) after chromatography. Reductive cleavage with LiAlH(4) allows direct access to chiral aldehydes, and treatment with MeLi gives chiral methyl ketones in excellent enantiopurity (> or = 94% ee). The auxiliary can be recovered in > 98% ee and recycled.

Doubly diastereoselective conjugate addition of homochiral lithium amides to homochiral alpha,beta-unsaturated esters containing cis- and trans-dioxolane units.

As part of a long-term goal directed towards the ab initio asymmetric synthesis of unnatural amino sugars, the doubly diastereoselective conjugate addition reactions of the antipodes of lithium N-benzyl-N-(alpha-methylbenzyl)amide to a range of homochiral alpha,beta-unsaturated esters containing cis- and trans-dioxolane units was investigated. These reactions resulted in "matching" and "mismatching" effects. In the "matched" cases a single diastereoisomer of the corresponding beta-amino ester (containing three contiguous stereocentres) is produced. Upon conjugate addition to a homochiral alpha,beta-unsaturated ester containing a cis-dioxolane unit, in the "mismatched" case it is the stereocontrol of the substrate which is dominant over that of the lithium amide, whilst upon addition to homochiral alpha,beta-unsaturated esters containing a trans-dioxolane unit the stereocontrol of the homochiral lithium amide is dominant. Hydrogenolytic N-deprotection of the beta-amino ester products of conjugate addition gives access to polyoxygenated beta-amino acid derivatives.

Highly diastereoselective anti-dihydroxylation of 3-N,N-dibenzylaminocyclohex-1-ene N-oxide.

Oxidation of 3-N,N-dibenzylaminocyclohex-1-ene N-oxide in the presence of Cl3CCO2H proceeds with high levels of anti-diastereoselectivity (97% de), with no competing side reactions, allowing access to 1,2-anti-2,3-anti-3-aminocyclohexane-1,2-diol after deprotection.

Stereocontrolled total synthesis of (-)-ephedradine A (orantine).

The stereocontrolled total synthesis of (-)-ephedradine A has been accomplished. The synthesis features an asymmetric C-H insertion reaction, an intramolecular ester-amide exchange reaction, and a Sharpless asymmetric aminohydroxylation reaction. Construction of the complex macrocyclic ring was performed by Ns-strategy and an intramolecular aza-Wittig reaction.