Staurosporine

Staurosporine (antibiotic AM-2282 or STS) is a natural product originally isolated in 1977 from the bacterium Streptomyces staurosporeus. It was the first of over 50 alkaloids to be isolated with this type of bis-indole chemical structure. The chemical structure of staurosporine was elucidated by X-ray analysis of a single crystal and the absolute stereochemical configuration by the same method in 1994.

Staurosporine was discovered to have biological activities ranging from anti-fungal to anti-hypertensive. The interest in these activities resulted in a large investigative effort in chemistry and biology and the discovery of the potential for anti-cancer treatment.

The main biological activity of staurosporine is the inhibition of protein kinases through the prevention of ATP binding to the kinase. This is achieved through the stronger affinity of staurosporine to the ATP-binding site on the kinase. Staurosporine is a prototypical ATP-competitive kinase inhibitor in that it binds to many kinases with high affinity, though with little selectivity. This lack of specificity has precluded its clinical use, but has made it a valuable research tool. In research, staurosporine is used to induce apoptosis. The mechanism of how it mediates this is not well understood. It has been found that one way in which staurosporine induces apoptosis is by activating caspase-3.

Staurosporine is the precursor of the novel protein kinase inhibitor midostaurin (PKC412). Besides midostaurin, staurosporine is also used as a starting material in the commercial synthesis of K252C (also called staurosporine aglycone). In the natural biosynthetic pathway, K252C is a precursor of staurosporine.

Biosynthesis
Indolocarbazoles belong to the alkaloid sub-class of bisindoles. Of these carbazoles the Indolo(2,3-a)carbazoles are the most frequently isolated; the most common subgroup of the Indolo(2,3-a)carbazoles are the Indolo(2,3-a)pyrrole(3,4-c)carbazoles which can be divided into two major classes - halogenated (chlorinated) with a fully oxidized C-7 carbon with only one indole nitrogen containing a β-glycosidic bond and the second class consists of both indole nitrogen glycosilated, non-halogenated, and a fully reduced C-7 carbon. Staurosporine is part of the second non-halogenated class.





The biosynthesis of staurosporine starts with the amino acid L-tryptophan in it zwitterionic form. Tryptophan is converted to an imine by enzyme StaO which is an L-amino acid oxidase (that may be FAD dependent). The imine is acted upon by StaD to form an uncharacterized intermediate proposed to be the dimerization product between 2 imine molecules. Chromopyrrolic acid is the molecule formed from this intermediate after the loss of VioE (used in the biosynthesis of violacein – a natural product formed from a branch point in this pathway that also diverges to form rebeccamycin. An aryl aryl coupling thought to be catalyzed by a cytochrome P450 enzyme to form an aromatic ring system occurs.



This is followed by a nucleophilic attack between the indole nitrogens resulting in cyclization and then decarboxylation assisted by StaC exclusively forming staurosporine aglycone or K252c. Glucose is transformed to NTP-L-ristoamine by StaA/B/E/J/I/K which is then added on to the staurosporine aglycone at 1 indole N by StaG. The StaN enzyme reorients the sugar by attaching it to the 2nd indole nitrogen into an unfavored conformation to form intermediated O-demethyl-N-demethyl-staurosporine. Lastly, O-methylation of the 4'amine by StaMA and N-methylation of the 3'-hydroxy by StaMB leads to the formation of staurosporine.

List of compounds closely related to Staurosporine

 * K252A
 * Stauprimide
 * Midostaurin
 * UCN01