The crude earthworm extract catalysed direct
asymmetric Mannich reactions
The asymmetric Mannich reaction is a powerful synthetic
strategy to prepare chiral b-amino ketones and aldehydes with
perfect atom economy through the loss of a molecule of water, and
the reaction products are versatile intermediates in the synthesis of
chiral amines [18]. The crude earthworm extract could catalyse
the direct asymmetric Mannich reactions in isopropanol/buffer
(Fig. 3). Various substituted aromatic aldehydes, arylamines and
cyclic or heterocyclic ketones participated in the reaction smoothly. Mannich products were obtained in yields of 42–83%
with diastereoselectivities of 43:57–87:13 (syn/anti) and enantioselectivities
of 44–76% ee (for syn isomers) under the optimized
conditions (Table 2, entries 1–6). In the absence of the crude
earthworm extract, the product was obtained only in 29% yield
with 38:62 dr (syn/anti) for the model Mannich reaction of 4-
nitrobenzaldehyde, aniline and cyclohexanone after 72 h (Table
2, entry 8), indicating that the crude earthworm extract
indeed catalysed the Mannich reaction in asymmetric manner.