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Studies Relating to the Configuration and Conformation of 3,5-Disubstituted Dihydro-2(3H)-furanones

✍ Scribed by Fischer, János ;Fodor, Tamás ;Dobay, László ;Kiss, Béla ;Tóth, Gábor ;Snatzke, Günther ;Ötvös, László

Publisher
John Wiley and Sons
Year
1989
Tongue
English
Weight
506 KB
Volume
1989
Category
Article
ISSN
0947-3440

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✦ Synopsis

Recently we reported on the Michael-type addition of dipeptides to 4-phenyl-4-oxo-2-butenoic acids and their esters". One of the products (1) was a convenient starting material for the preparation of new angiotensin-converting enzyme (ACE) inhibitors. In this paper we describe the lactone derivatives of enalpri12).

Reduction of the carbonyl group in 1 afforded two epimeric alcohols, 2a and 2b, which could not be separated, due to rapid partial lactonization to 3a and 3b even on chromatography3'. The ratio of epimers depended on the method of reduction. Thus, reduction with KBH4 afforded 2a and 2b in a ratio of 2: 1, Na(CN)BH3 gave a 1 :2 ratio, while with catalytic hydrogenation over Pd/C the ratio was 1 :I. In the latter case over-reduction to a CH2 group is possible.

Lactonization becomes complete on heating 2a and 2b in acetic acid at 50-60°C. There is a significant difference between the lactonization rates of the two epimers. While 1 -2 hours is sufficient for the lactonization of 2a, complete transformation of 2 b requires 24 hours (Scheme 1).

By equilibration in tBuOH/tBuOK it was demonstrated that with 3,5-disubstituted dihydro-2(3 H)-furanones the cis configuration was preferred ' ). Configuration assignment was *I Chemical name of enalapril: (lS)-N-[l-ethoxycarbonyI-3-phenylpropyll-(5')-alanyl-(S)-proline maleate.

N-(tert-Butoxycarbony1)-(S)-lysyl-(S)-proline tert-Butyl Ester

(5): This was prepared according to ref."I. Benzyl (E)-4-Oxo-4-phenyl-2-butenoate (6): This was also prepared by a known ( I S ) -N-[I-(Benzyloxycarbonyl)-3-oxo-3-phenyl-propyl]-N"-(tert-butoxycarbony1)-(S)-lysyl-(S)-proline tert-Bzityl Ester Oxa-') J. Fischer, T. Fodor, L. Dobay, Monatsh. Chem. 119 (1988) 645.

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