On Cardioactive Steroids. VIII. The Synthesis of Bufalin and Resibufogenin Isomers

Abstract

Summarya-Isobufalin') (1) and pisoresibufogenin') (3) have been synthesized from testosterone by a method which features a novel oxidative furan to pyrone transformation.

On cardioactive steroids. XII. The synthesis of (natural) bufalin and α′‐isobufalin

“…4-(3'~-Benzyloxy-5'P-androst-ll'-en-i7'8-yl) furan-2-carbaldehyde Ethylene Acetal (3). Compound IX [2] (1.93 g) in pyridine (7.5 ml) was cooled in an ice-bath and treated with SOCI, (517.9 mg) for 30 min. The mixture was stirred at r.t. for 30 min and then diluted with Et,O.…”

“…-The first four steps of our bufalin synthesis were identical with the already described [2] preparation of fl-isoresibufogenin 111, and they are, for the sake of completeness, shown in Scheme 1 (formulae IV-IX) together with the yields obtained.…”

“…-In [2] we have described a relatively simple synthesis of the bufalin and resibufogenin isomers 1-111 ') in which we utilized an adaptation of our furan strategy for cardenolides [3]. The pharmacological study of these compounds and their dihydro derivatives submitted as glucosides yielded interesting results [4].…”

“…Its spectral properties left no doubt that the a-pyrone construction was now complete. The introduction of the 14'fl-OH-group was performed as described previously by the modified method of Engel (cJ [2] [3]), and the product, 3-o-benzylbufalin (8), was isolated in a yield of 70% and crystallized from Et,O/CH,Cl,. Finally, debenzylation of 8 with Pd(OH),/C [9], a method which we have used previously in our synthesis of the isobufalins [2], yielded 70% of the crystalline (m.p.…”

A selective synthesis of 4-bromo-2-furancarboxaldehyde and its pinacolborane derivative

“…Ethylene acetal of 4-bromo-2-furancarboxaldehyde (4) is the starting material for the synthesis of important biologically active compounds such as the cardioactive cardenolide steroids [1][2][3][4][5][6]. The pinacolborane derivative (5) of the above mentioned material could be used to synthesize these cardioactive steroids in a Suzuki reaction with enol triflates [7][8].…”