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3.3. Isolation and Characterization of Bioactive Compound The active compound was found to be intracellular, hence mycelial extract was subjected to bioactivity guided isolation and purification as mentioned in 2.7. The active compound was able to adsorb on HP-20 resins. Further fractionation of crude material using petroleum ether helped removing the impurities and subsequent dichloro- methane fraction was found to be active. The pure compound was finally isolated by silica gel chromatography followed by preparative HPLC using RP-18 resin. The characterization of isolated compound was carried out based on data obtained from mass, IR and 1 H NMR spectra (Figures 3-5). In 1 H NMR spectra, the signals at δ 7.8 and 7.35 were assigned for protons attached at C-3 and C-5 respectively. Proton at unsaturated C-7 appeared at δ 8.13 due to nitrogen and OH group being in proximity. The aromatic protons associated with other pyridine ring were assigned in the range of δ 7.4 - 8.3. The O-methyl group showed a singlet for 3 H at δ 3.9. Structural confirmation was done by comparing the spectral values with the published data [19]. Based on the data, the ac- tive compound was characterized as Caerulomycin A. Figure 6 and its chemical properties are shown in Table 5. From the final yield of the isolated compound (20 mg from 8.5 L broth), the back calculated titer in the har- vested broth was estimated as 2.3 mg/L. In order to simplify the extraction method for scale-up purification, the whole broth extraction with equal quantity of ethyl acetate was attempted. Caerulomycin A was found to be completely extractable in ethyl acetate hence this method could be used for large scale extraction batches. |
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3.3. 生物活性化合物的分离与鉴定 生物活性化合物发现于细胞内，因此，根据上述在2.7中所述的生物活性指导的方法对菌丝体提取物进行分离和纯化。活性化合物能被HP-20树脂吸附。用石油醚对粗制品进一步分馏以帮助除去杂质，随后的二氯甲烷组分发现具有生物活性。先用硅胶柱层析、再用RP-18树脂进行制备型HPLC，最终分离得到纯的化合物。所分离化合物的鉴定是基于质量、红外线光谱和1H NMR光谱所得到的数据（图3-5）。在1H-NMR光谱中，在δ7.8和7.35处的信号被定为分别连于C-3和C-5上的质子。由于氮和OH基团很近，所以位于不饱和C-7上的质子出现在δ8.13。与其他吡啶环相连的芳香质子位于δ7.4－8.3之间。 O－甲基在δ3.9处呈单峰。通过将光谱数据与已发表的数据[19]比较以进行结构确认。根据该数据，将活性化合物被鉴定为青蓝霉素。（结构见）图6和它的化学性质见表5。根据所分离的化合物的最终产率（从8.5 L液体培养基中得到20毫克），往回推算出收获培养基中的滴度约为2.3毫克/升。为了简化提取方法以进行规模化纯化，尝试用等量乙酸乙酯对全培养基进行提取。发现青蓝霉素可以完全被乙酸乙酯萃取，因此可用该方法进行大规模批次提取。 |
2楼2014-10-28 00:21:47
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