Haruhisa Shirahama

Isolation and structure of aromelic acid A and B. New kainoids of clitocybe acromelalga

Abstract A minute amount of the new kainic acid-like amino acids, acromelic acid A (ca. 110 μg) and B (ca. 40 μg), was isolated from the poisonous mushroom Clitocbe acromelalga and their structures were inferred to be 1 and 2 respectively by spectral analyses.

Structure of lampterol (illudin S)

Abstract The structure of lampterol, an antitumor substance isolated from Lampteromyces japonicus has been established in I.

An efficient approach toward pyrrolidinyllactone system characteristic of the Stemona alkaloids. Lewis acid catalyzed stereoselective reaction of N-benzyloxycarbonyl-2-methoxypyrrolidine with 3-methyl-2-trimethylsilyloxyfuran

Abstract Pyrrolidinyllactone system 7 , common partial structure presented in most Stemona alkaloids, was stereoselectively prepared by two-step sequence: i) syn -selective condensation of N -benzyloxycarbonyl-2-methoxypyrrolidine ( 8 ) with 3-methyl-2-trimethylsilyloxyfuran ( 9 ) catalyzed by Lewis acids; ii) diastereoselective hydrogenation of the product 10 (NaBH 4 , NiCl 2 / MeOH).

Conformationally selective transannular cyclizations of humulene 9,10-epoxide. Synthesis of the two skeletally different cyclohumulanoids: dl-bicyclohumulenone and dl-africanol

Two cyclohumulanoids, dl-bicyclohumulenone (4) and dl-africanol (7 were synthesized through newly developed conformationally selective transannular cyclization of humulene 9,10-epoxide (2). The epoxide 2 was converted to a bicyclohumulenediol diacetate 3a in 70% yield by treatment with BF3·OEt2-Ac2O, while treatment of 2 with trimethylsilyl trifluoromethansulfonate gave an africen-10-ol (5a and 5b) in 80% yield. The two intermediates 3a and 5a furnished the natural products 4 and 7 in 30 and 8 % yield from 2 respectively.

Conformational aspects of caryophyllene. Population of stable conformers and ring inversion barrier of trans cyclononene ring portion

Abstract Cmr measurements of caryophyllene revealed two major conformers equilibrating in a ratio 76:24 at room temperature. The energy ordering of four possible conformers of caryophyllene predicted by molecular mechanics calculations agrees well with the experimental observation. The barrier of interconversion between the two conformers was determined as 16.25 kcal/mol.

β-Phenylselenoalanine as a dehydroalanine precursor–efficient synthesis of alternariolide (AM-toxin I)

Alternariolide (AM-toxin) is synthesized in 44% overall yield from L-2-amino-5-(4-methoxyphenyl)pentanoic acid; D-β-phenylselenoalanine is used as the dehydroalanine precursor.

Synthesis of acromelic acid A, a toxic principle of clitocybe acromelalga.

Abstract Acromelic acid A, a toxic principle of Clitocybe acromelalga , was synthesized from l -α-kainic acid. The synthesis established the previously inferred structure, and determined the absolute configuration as shown by 1 .

Synthetic studies on virantmycin. 1. Total synthesis of (±)-virantmycin and determination of its relative stereochemistry

Abstract The efficient and stereospecific route to the tetrahydroquinoline ring models 3 and 4 of virantmycin has been developed by means of an intramolecular nitrene addition reaction as a key step. In the NOE experiments of 4 and 3 we revealed that a ring inversion occurs in their piperidine ring system and determined the relative stereochemistry by capturing each half-chair conformer as cyclic carbamates 26 and 27 , respectively. Utilizing this protocol total syntheses of (±)- 1 and its diastereomer (±)- 2 have been accomplished and the relative stereochemistry of virantmycin has been established as shown in 1 .

Efficient construction of 8-membered ring framework of vinigrol through SmI2-induced coupling cyclization

Abstract The 8-membered ring framework of vinigrol, a unique tricyclic diterpene isolated as a novel antihypertensive compound from a culture of Virgaria nigra , was efficiently synthesized employing an SmI 2 -induced intramolecular coupling. It is particularly noteworthy that the 8-membered carbocycle was cyclized in quantitative yields under non-high-dilution conditions .

Effective deprotection of 2-(trimethylsilylethoxy)methylated alcohols (SEM ethers). Synthesis of thyrsiferyl-23 acetate

Abstract New conditions for effective cleavage of SEM ethers were developed (TBAF/HMPA in the presence of MS 4A) and usefulness of this reaction was demonstrated by the synthesis of thyrsiferyl-23 acetate.