Natsuko Kurokawa

Total synthesis of echinocandins. I: Stereocontrolled syntheses of the constituent amino acids

Figure 1. (a) UV-visible absorption spectrum of pyrimido[5,4-g]pteridine N-oxide 1 (5 X M ) in MeCN. (b) Difference spectrum of the mixture of 1 (5 m M ) and D M A (250 m M ) vs. 1 (5 m M ) in MeCN. (c) Wavelength dependence (presented by the yield of M M A ) in the photochemical demethylation of D M A by 1. A solution of 1 (5 m M ) and D M A (50 m M ) in MeCN was irradiated by using a grating monochromator (JASCO Model CRM-FA) with 2-kW Xe lamp and 4-nm band width under argon atmosphere for 2 h.

Synthesis of the serine equivalent, (2R) and (2S)-amino-3-butenol derivatives. Synthetic approaches to the metal chelating poly-amino acid, «aspergillomarasmine A»

Chiral synthons, equivalent to the C3 amino acid serine, were synthesized in both (2R) and (2S) form from D or L-methionine respectively; Utilization of this synthon in the construction of metal chelating poly-amino acid aspergillomarasminea A skeleton is presented.

Efficient syntheses of naturally occurring 3,4-dihydroxyprolines: Electrophile-mediated lactonization of 2-amino-3-hydroxy-4-pentenoic acid derivatives

Abstract Stereospecific conversion of β-hydroxyallylglycine derivatives into (2 S , 3 R , 4 R ) 1 and (2 S , 3 S , 4 S ) 2 via halo- or mercuri-lactonization has been described.

Synthesis of (+)-galantinic acid, a constituent amino acid in the peptide antibiotic galantin I, via the stereoselective epoxidation of a chiral serine equivalent

Abstract Epoxidation of (2 R )- t -butoxycarbonylamino-3-butenol afforded, in a highly stereo-selective manner, a threo -3,4-epoxy-2-aminobutanol derivative which was successfully converted to the unusual amino acid (+)-galantinic acid in 8 steps via regiospecific epoxide ring opening with divinyl cuprate.

Synthetic studies on antifungal cyclic peptides, echinocandins. Stereoselective total synthesis of echinocandin D via a novel peptide coupling

Abstract Synthetic studies on the novel fungicidal oligopeptides, echinocandins (1b and 1c), are described. The constituent amino acids 5–8 were synthesized in a stereocontrolled manner from the chiral starting materials, 5a, 6a and 7a, respectively. The coupling of these amino acids was characterized by the use of unprotected amino acid as the C-terminal and 2-pyridyl thiol ester as the N-terminal, and the coupling was performed in the presence of 1-(trimethylsilyl)imidazole (TMSIm) or a catalytic amount of tert-amine to give C-terminal free dipeptides, 14 and 16a, respectively, which were converted to the pentapeptide 17a, a common intermediate for the synthesis of 1b and 1c. The synthesis of 1c was achieved by the cyclization of the hexapeptide 24b.

The palladium(II)-assisted syntheses of (±)α-(methylenecyclopropyl)glycine and (±)trans-α-(carboxycyclopropyl) glycine, two bioactive amino acids.

Abstract Title compounds 1 and 2 have been synthesized efficiently from β-hydroxyallylglycine derivative 3 via the Pd(II)-catalyzed reactions.

N-carboxylate ion equivalent. II. Novel transformations of N-benzyloxycarbonyl (Z) group and N-allyloxycarbonyl group into N-t-butyldimethylsilyloxycarbonyl intermediate

Abstract N-Benzyloxycarbonyl compounds and N-allyloxycarbonyl compounds were efficiently converted to the corresponding t -butyldimethylsilyloxy-carbonyl compounds by t -butyldimethylsilane in the presence of Pd(II) catalyst.

Effects of compounds related to β-hydroxyglutamic acid (BHGA) on identifiable giant neurones of an African giant snail (Achatina fulica Férussac)

The present study aimed to further elucidate the pharmacological features, with respect to sensitivity to L-BHGA agonists, of the receptors sensitive to beta-hydroxy-L-glutamic acid (L-BHGA) in five Achatina giant neurones: PON (periodically oscillating neurone), d-RPLN (dorsal-right parietal large neurone), VIN (visceral intermittently firing neurone), RAPN (right anterior pallial neurone) and v-RCDN (ventral-right cerebral distinct neurone). Of these neurones, d-RPLN and RAPN were depolarized by L-BHGA, while PON, VIN and v-RCDN were inhibited. Threo-beta-hydroxy-DL-aspartic acid markedly depolarized d-RPLN and RAPN (effective potency quotient (EPQ) in relation to the more effective L-BHGA isomer: 1 for d-RPLN and 0.3 for RAPN). This compound produced only slight inhibitory effects on PON, VIN and v-RCDN with EPQs calculated to be less than 0.03, less than 0.03 and 0.03, respectively. On the other hand, erythro-beta-hydroxy-DL-aspartic acid at 10(-3) M was almost ineffective, except on v-RCDN where it elicited some slight inhibitory effects (EPQ: 0.01). L-Aspartic and D-aspartic acid at 10(-3) M, also had almost no effect except for slight effects of D-aspartic acid on d-RPLN (EPQ: 0.1). N-Methyl-L- and N-methyl-D-aspartic acid were slightly effective only on v-RCDN (EPQ: less than 0.01 and 0.01, respectively). The other compounds, including beta-hydroxypyrroglutamic acid (cyclic BHGA) and proline derivatives, were almost ineffective at 10(-3) M; very weak effects were occasionally observed on some neurones.(ABSTRACT TRUNCATED AT 250 WORDS)