Castanospermine is an indolizidine alkaloid first isolated from the seeds of Castanospermum australe.

[3] It is a potent inhibitor of some glucosidase enzymes[4] and has antiviral activity in vitro and in mouse models.

[5] The castanospermine derivative celgosivir is an antiviral drug candidate that as of 2009 was in development for possible use in treating hepatitis C virus (HCV) infection.

[7][8][9] In the alternate pathway L-Lys cyclizes and forms the enamine, which reduces to L-pipecolic acid.

The molecule is then further hydroxylated to form the final product castanospermine.