Kunisuke Okada

Total synthesis of (±)-surugatoxin☆

Abstract Total synthesis of surugatoxin 1 , isolated from the toxic Japanese ivory shell ( Babylonia japonica ), was achieved from 6-bromoisatin by a stepwise ring construction involving two key steps: the stereospecific cyclization ( 17 → 18 ) and hydration ( 33b → 1 ).

Total synthesis of neosurugatoxin

Abstract Total synthesis of neosurugatoxin 2 , having a strong affinity for nicotinic receptors, in described.

Total synthesis of (-+)-surugatoxin

Abstract Total synthesis of surugatoxin 1, isolated from the toxic Japanese ivory shell ( Babylonia japonica ), was achieved from 6-bromoisatin by stepwise ring construction involving two key steps: the stereospecific cyclization (9→10) and hydration (17→1).

Synthesis of (±)-prosurugatoxin and ring transformation of prosurugatoxin into surugatoxin

Abstract Synthetic identification of prosurugatoxin and data indicating a possible mechanism for the ring transformation of prosurugatoxin into surugatoxin are presented.

Asymmetric synthesis of the pentacyclic ring system of Aspidosperma alkaloids

Abstract The asymmetric synthesis of pentacyclic compound 13, a known intermediate in the synthesis of l-acetylaspidospermidine, was conducted via the condensation of 2-hydroxytryptamine with chiral C9 lactone 9, readily available from triol 4.

Model experiments on surugatoxin synthesis. an approach in the construction of the pentacyclic ring system

Synthesis of the ethyl ester 2a of the debromo-aglycone of surugatoxin 1 has been achieved in 10 steps starting from readily available ethyl 2-(2-oxo-3-indolenyl)-3-oxo-4-phthalimidobutyrate 3.

Total synthesis of (−)-vallesamidine

Abstract A new synthetic method of (−)-vallesamidine, including a unique 2,2,3-trialkylindoline skeleton, is developed by reductive radical cyclization reaction from the 2,3-dialkylindole derivative, which has been known to be an intermediate for the synthesis of aspidospermidine.

2-MERCAPTOBENZOTHIAZOLYLMETHYLPYRROLE AS A NEW MEANS FOR THE SYNTHESIS OF PYRROMETHANES UNDER NEUTRAL CONDITIONS

Abstract The coupling reaction of 2-mercaptobenzothiazolylmethylpyrrole 4b with α-free pyrrole 2b in the presence of silver (I) triflate proceeds smoothly at room temperature to give pyrromethane 1b in excellent yield. 4b reacts rapidly with pyrromethane 1b under similar neutral conditions to afford symmetric pyrromethane 7 in preparative yield.

Isomerization of uroporphyrinogen I octamethyl ester through spiro-pyrrolenine intermediate

Abstract Treatment of uroporphyrinogen I octamethyl ester with 2-mercaptobenzothiazolylmethyl pyrrole derivative in the presence of silver (I) trifrate under anaerobic condition in dichloromethane for 20 h, followed by aerial oxidation of the products, gave a statistical mixture of uroporphyrin I∼IV octamethyl esters. It was proposed that this transformation proceeds through a spiro-pyrrolenine as a key intermediate.

New method for the synthesis of pyrromethanes

Abstract Coupling reaction of 2-mercaptobenzothiazolylmethylpyrrole with α-free pyrrole in the presence of silver(I) triflate proceeds smoothly at room temperature to give a pyrromethane in excellent yield. The azafulvenium ion, an active form that reacts with α-free pyrrole, also reacts with pyrromethane rapidly under similar neutral conditions to afford an equilibrated mixture of pyrromethanes in good yield.