Minimycin

Minimycin (MIN) is a C-nucleoside antibiotic structurally related to pseudouridine, and indigoidine is a naturally occurring blue pigment produced by diverse bacteria. Although MIN and indigoidine have been known for decades, the logic underlying the divergent biosynthesis of these interesting molecules has been obscure. Here, we report the identification of a minimal 5-gene cluster (min) essential for MIN biosynthesis. We demonstrated that a non-ribosomal peptide synthetase (MinA) governs "the switch" for the divergent biosynthesis of MIN and the cryptic indigoidine. We also demonstrated that MinCN (the N-terminal phosphatase domain of MinC), MinD (uracil phosphoribosyltransferase), and MinT (transporter) function together as the safeguard enzymes, which collaboratively constitute an unusual self-resistance system. Finally, we provided evidence that MinD, utilizing an unprecedented substrate-competition strategy for self-resistance of the producer cell, maintains competition advantage over the active molecule MIN-5'-monophosphate by increasing the UMP pool in vivo. These findings greatly expand our knowledge regarding natural product biosynthesis.

IM-2 [(2R,3R,1'R)-2-(1'-hydroxybutyl)-3-(hydroxymethyl)butanolide] of Streptomyces sp. strain FRI-5 is one of the butyrolactone autoregulators of Streptomyces species and triggers production of blue pigment as well as the nucleoside antibiotics showdomycin and minimycin. A tritium-labeled IM-2 analogue, 2,3-trans-2(1'-beta-hydroxy-[4',5'-3H]pentyl)-3-(hydroxymethyl)butano lide ([3H]IM-2-C5; 40 Ci/mmol), was synthesized for a competitive binding assay, and an IM-2-specific binding protein was found to be present in the crude cell extract of Streptomyces sp. strain FRI-5. During cultivation for 24 h, the specific IM-2-binding activity increased rapidly, reached a plateau at 10 to 14 h, and declined sharply thereafter, showing only 6% activity after 24 h of cultivation. A Scatchard plot of the binding data demonstrated that the dissociation constant (Kd) for [3H]IM-2-C5 was 1.3 nM, while the Kd for a 3H-labeled virginiae butanolide (VB) analogue, 2-(1'-alpha-hydroxy-[6',7'-3H]heptyl)-3-(hydroxymethyl)butanolide ([3H]VB-C7), another butyrolactone autoregulator possessing the opposite configuration at C-1' was 35 nM. Furthermore, at a 15-fold molar excess, the effectiveness of several autoregulators as nonlabeled competitive ligands against [3H]IM-2-C5 was IM-2 type > VB-C type >> A-factor type, indicating that the binding protein in Streptomyces sp. strain FRI-5 is highly specific toward IM-2. Ultracentrifugation showed that the IM-2-binding protein is present almost exclusively in the 100,000 x g supernatant fraction, indicating that the binding protein is a cytoplasmic soluble protein. The binding protein was purified by ammonium sulfate precipitation, DEAE-Sephacel chromatography, Sephacryl S-100 HR gel filtration, DEAE-5PW high-performance liquid chromatography (HPLC), and phenyl-5PW HPLC. The apparent Mr of the native IM-2-binding protein as determined by molecular sieve HPLC was about 60,000 in the presence of 0.5, 0.3, or 0.1 M KCl, while by sodium dodecyl sulfate-polyacrylamide gel electrophoresis it was about 27,000, suggesting that the native binding protein is present in the form of a dimer.

Oxazines have brought much synthetic interest due to their extensive biological activities. These are the important category of heterocycles, which may be formally derived from benzene and its reduction products by convenient substitution of carbon (and hydrogen) atoms by nitrogen and oxygen. In the last few decades, oxazine derivatives have documented as worthy synthetic intermediates and also blessed with notable sedative, analgesic, anticonvulsant, antipyretic, antimicrobial, antitubercular, antimalarial, antioxidant, and anticancer activities. Nowadays, it is important to develop new classes of compounds with more effective mechanisms due to drug resistance activity in which the ability of drug to effectively treat disease can be reduced. The aim of the article is to collect and make a more generalized review on the synthesis of oxazine derivatives and their pharmaceutical and biological activities. We hope this review will provide ample references for the researchers concerned with azines in generally and oxazines in particular.