Abstract: The invention provides chemically modified proteins having a group of the formula: ##STR1## wherein R represents a hydrogen atom or a lower alkyl, m represents an optional positive integer and n represents an integer 1 to 4, the group being bonded to at least one primary amino group of the protein, and a method of producing the same. The chemically modified proteins according to the invention can be produced by reacting a protein with an imidoester of the formula: ##STR2## wherein R, n and m are as defined above, R' represents a group constituting an imidoester with an adjacent imidoyl group. The chemically modified proteins according to the invention are useful as drugs, among others.

Abstract: An enantioselective synthesis of 1,3,4,6,7,12b(S)-hexahydro-2H-benzo[b]furo[2,3-a]quinolizin-2-one provides a key intermediate for the preparation of the .alpha..sub.2 -adrenergic antagonist (2R,12bS)-N-(1,3,4,6,7,12-hexahydro-2H-benzo[b]furo[2,3-a]quinolizin-2-yl) -N-methyl-2-hydroxyethanesulfonamide hydrochloride, useful as an anti-depressant.