Baeyer-Villiger oxidase; part of the ergochrome gene cluster responsible for the typical purple-black color of the ergot sclerotia (PubMed:28955461). The ergochrome gene cluster produces several ergot pigments including the yellow ergochrome secalonic acid and its derivatives, as well as the red anthraquinones endocrocin and clavorubin (PubMed:28955461). The pathway begins with the synthesis of atrochrysone thioester by the polyketide synthase (PKS) CPUR_05437 (By similarity). The atrochrysone carboxyl ACP thioesterase CPUR_05436 then breaks the thioester bond and releases the atrochrysone carboxylic acid from CPUR_05437 (By similarity). The atrochrysone carboxylic acid is then converted to atrochrysone which is further transformed into emodin anthrone (By similarity). The next step is performed by the anthrone oxygenase CPUR_05434 that catalyzes the oxidation of emodinanthrone to emodin (By similarity). Emodin is further modified to yield monodictyphenone via several steps involving CPUR_05427, CPUR_05428, CPUR_05429 and CPUR_05430 (By similarity). The short chain dehydrogenase/reductase CPUR_05418 then catalyzes the C-5 ketoreduction to give the xanthone skeleton of the monomeric units (PubMed:32105084). Ergochromes formation requires further dimerization steps of different xanthone units, probably catalyzed by the cytochrome P450 monooxygenase CPUR_05419 (PubMed:28955461). CPUR_05425, CPUR_05426 and CPUR_05431 are unique to Claviceps, thus it is likely that they are involved in further modification of xanthone units or in their dimerization (PubMed:28955461). The yellow ergochromes and the red anthraquinone pigments endocrocin and clavorubin are products from the same PKS derived precursors and the latter are likely shunt products in the pathway of xanthone biosynthesis (PubMed:28955461). It is proposed that atrochrysone carboxylic acid released from the PKS CPUR_05437 can also0 be converted to endocrocin anthrone which is further oxidized into endocrocin by CPUR_05435 (By similarity). Endocrocin could be then modified to clavorubin, possibly by CPUR_05423 and CPUR_05431 (PubMed:28955461). Clavorubin is the principal anthraquinone metabolite produced by the cluster with a much higher yield compared to endocrocin (PubMed:28955461). Pigment biosynthesis. Expression correlates with the formation of the sclerotia and thus the pigment production and is directly regulated by the cluster-specific activator CPUR_05433 (PubMed:28955461). Belongs to the questin oxidase family.