Arachidonic acid has been converted by aerobic oxidation with lipoxygenase (ex soybean) as catalyst and in the presence of sodium borohydride in a one-pot procedure (1 g scale) into (52,82.11Z.13€) (1 5S)-15-hydroxyeicosa-5.8.1 1,13-tetraenoic acid. The methyl (1 5s) -1 5-hydroxyeicosatetraenoate or its p-nitrobenzoate derivative may be epoxidised with rn-chloroperbenzoic acid to afford mixtures of the 5,6-, 8.9-, 11.1 2-, and 13,14-monoepoxides together with a mixture of bisepoxides. The methyl (1 5s) -1 5-(p-nitrobenzoyloxy)eicosatetraenoate epoxides can be separated by preparative t.1.c. The methyl (1 5S)-15-(mercaptoacetoxy)eicosatetraenoate has been prepared from the chloroacetate derivative of the methyl (1 5s) -1 5-hydroxyeicosatetraenoate by reaction with potassium thioacetate followed by selective hydrolysis of the thioester function.
The oxidation of 4.5.5-trimethyl-1 -pyrroline 1 -oxide (I) with lead tetra-acetate gives 1 -acetoxy-4,5,5-trimethyl-2-pyrrolidone ( I I b ) in 64% yield : with an excess of potassium permanganate the major product was 3.4-dimethyl-4-nitropentanoic acid (IVa). 1 -Hydroxy-4,5,5-trimethyl-2-pyrrolidone ( I I a ) w a s cleaved upon treatment with potassium permanganate or lead tetra-acetate and gave novel compounds derived from two molecules of (IIa). The existence of a nitroso-acylating species ( V I I I ) in these oxidations w a s confirmed by isolation of nitrosoamides on addition of arnines to the oxidation media.A VARIETY of reagents have been used to oxidise nitrone~,l-~ and such reactions have been reviewed.6-8 Lamchen reported that oxidation of l-pyrroline l-oxides, unsubstituted at the 2-position, with iron (111) chloride gave l-hydroxy-2-pyrrolidones.Oxidation of the same compounds with sodium periodate has indicated that oxidative cleavage to the nitroso-acid proceeds by way of the same hydroxamic acid. The following scheme has been proposed for the reaction :
Acetylation and benzoylation of 2-amino-5.5-dimethyl-A1-pyrroline 1 -oxide (I) gave 3-substituted products.Reaction mechanisms are discussed. Schotten-Baumann benzoylation of the same compound gave Z-benzamido-2-benzoyloxy-I -hydroxy-5,5-dimethylpyrrolidine (Xa), the derived 1,2-dibenzoate (Xb), and a 3-substituted by-product. Contrary to an earlier report, aryl isocyanates react with the pyrroline oxide (I) to give Z-arylcarbamoylimino-1 -hydroxy-derivatives.IT has been reported that 2-amino-5,5-dimethyl-A1pyrroline l-oxide is inert to acylating agents. This claim was later refuted by Forrester and Thomson,2 who found that on acetylation, benzoylation, or methylation, the predicted products could be isolated. We have re-examined the first two reactions, as we thought that under these conditions certain rearrangements might be observed. Previous work had shown3 that, under parallel conditions, migration of an acyloxygroup from the pyrroline nitrogen atom to position 3 can result.Acetylation under mild conditions gave the monoacetyl derivative (IIa), as earlier reported2 In contrast, d; R = NH*CGH,.N02-p e ; R = NH.C,H,CI-p CI 1 (1) a ;
The relatively rapid formation of pyrazoline adducts is a serious side reaction in the esterification of 15-oxo-PGF2alpha with ethereal diazomethane under conditions used routinely in the chemical derivatization of prostaglandins.
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