First total synthesis of pseudodistomin tetrahydroacetate

Alkaloids from Marine Ascidians

“…Pseudodistomins A ( 253 ) and B ( 254 ), from Pseudodistoma kanoko , represent the first piperidine alkaloids obtained from marine sources [ 164 ]. The structure of the side chains of 253 and 254 has been revised after the first disclosure of the molecules [ 165 , 166 ], while the stereostructure of the piperidine nucleus has been established by synthesis of their tetrahydroacetyl derivatives [ 167 , 168 ]. Other members of the group have been successively isolated, from other Pseudodistoma species, including pseudodistomin C ( 255 ), with the absolute configuration at C-4 and C-5 opposite to those found in 253 and 254 [ 169 ], and pseudodistomins D–F ( 256–258 ) ( Figure 27 ) [ 170 ].…”

Oxidation of Oxazolines and Thiazolines to Oxazoles and Thiazoles. Application of the Kharasch−Sosnovsky Reaction

“…4-Carbomethoxy-2-phenyl-2-oxazoline, 13a. Prepared as described in the general procedure using 2.74 g (16 mmol) of benzimidate hydrochloride, 2.74 g (17.6 mmol) of racemic serine methyl ester and 27 mL of CH 2 Cl 2 . Flash chromatography on SiO 2 using hexane/ethyl acetate (80:20) gave 13a as a colorless oil.…”

“…4-Carbomethoxy-2-phenyl-2-oxazole, 14a. To 4-carbomethoxy-2-phenyl-2-oxazoline (0.30 g, 1.46 mmol) and benzoyl peroxide (20 mg, 0.082 mmol) was added 10 mL of dry benzene (0.15 M) and the reaction mixture brought to gentle reflux for 15 min. To this was added NBS (0.311g, 1.75 mmol) and further refluxed for 1.5 h. The flask was cooled, and the contents were poured over crushed ice.…”

Pyrrole, pyrrolidine, pyridine, piperidine, and azepine alkaloids

“…43 The scheme involves two photochemical steps; first the reductive photocyclization of enamide (74), followed by a radical allylation of the 2-thio-S-lactam (75) to yield the a-allyllactam (76) as the major isomer. A quite different approach has been used in the preparation of the free base (82) (Scheme 17).44 The use of the 4-trimethylstannyl blocking group in the starting material (78) allows alkylation at C-2 in 84% yield.…”

“…40 The second method, from L-sorbose, is even shorter, requiring the isolation of just two intermediate^.^^ A stereoselective synthesis of the galactosidase inhibitor ( + )galactostatin (7 1) and its enantiomer has been accomplished in eleven steps from D-and L-serine, re~pectively.~~ The structures of the antineoplastic pseudodistomins A (72) and B (73), isolated from the Okinawan tunicate Pseudodistoma kanoko, have been confirmed by synthesis of the tetrahydroacetate (77) Reagents : i, 2-phenyloxazol-5-yl chloroformate, NEt, ; ii, hv, NaBH (Scheme 1 6). 43 The scheme involves two photochemical steps; first the reductive photocyclization of enamide (74), followed by a radical allylation of the 2-thio-S-lactam (75) to yield the a-allyllactam (76) as the major isomer. A quite different approach has been used in the preparation of the free base (82) (Scheme 17).44 The use of the 4-trimethylstannyl blocking group in the starting material (78) allows alkylation at C-2 in 84% yield.…”