Absolute configuration of NFAT-133, an aromatic polyketide with immunosuppressive and antidiabetic activity from actinomycetes
Absolute configuration of NFAT-133, an aromatic polyketide with immunosuppressive and antidiabetic activity from actinomycetes
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DOI：
10.1038/ja.2015.80
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发表时间：
2016-01-01
影响因子：
3.3
通讯作者：
Igarashi, Yasuhiro
中科院分区：
文献类型：
--
作者：
Yang, Yanan;Yu, Linkai;Igarashi, Yasuhiro
NFAT-133（1）是一种相对较小的芳香族聚酮化合物，分离自放线菌属Dacetylsporangium 1和链霉菌属（图1）。2这种三烷基取代的苯衍生物带有三个连续的立体中心，包括在烷基侧链上的羟基和甲基取代，但相对和绝对构型仍然未知。NFAT-133（1）是一种具有免疫抑制和抗糖尿病活性的药物分子。它抑制由NFAT（活化T细胞核因子）介导的转录，导致抑制IL-2（白细胞介素-2）表达和随后的T细胞增殖。1此外，该化合物刺激骨骼肌细胞的葡萄糖摄取。db/db小鼠的体内实验证明了其降低血糖和胰岛素的功效，而没有体重增加，2体重增加是目前使用的噻唑烷类抗糖尿病药物的副作用（在Kulkarni-Almeida等人，2 NFAT-133的结构在C2/C3双键方面不正确）。为了探索NFAT-133（1）的化学修饰衍生物的生物效力，有必要指定其绝对构型。在我们正在进行的关于链霉菌物种中次级代谢产物多样性的化学研究计划中，注意到在卡纳塔克邦链霉菌NBRC 13051的培养提取物中产生3 - 5个1。该菌株在液体培养基中生长，从培养物提取物中纯化几个步骤得到纯形式的1。来自菌株NBRC 13051的1的1H和13C NMR光谱数据与先前报道的NFAT-133的那些相同（表1）。1，2立体化学分析开始于对C11的仲羟基应用手性各向异性方法6。通过用（S）-和（R）-MTPACl处理1的酯化，分别得到双-（R）-和（S）-MTPA酯（2a和2b）。通过从2b的1H NMR化学位移δ H中减去2a的1H NMR化学位移δ H来计算Δ δ S-R值。虽然H12和H17的Δ δ S-R值为零，但H14观察到正值，H2、H3、H10和H16观察到负值。[6]因此，C11的绝对构型确定为R。通过对偶合常数的分析，确定了C10和C12的相对构型。较大的3JH10、H11（7.0 Hz）和较小的3JH11、H12值（3.9 Hz）分别表示H10/H11和H11/H12的反和顺关系（图2）。该归属与NOESY光谱中H10和H17之间以及H12和H16之间观察到的NOE非常一致（图3）。此外，H3和H10、H8和H11以及H2和H5之间的NOE表明，C4和C9处的侧链从芳族核延伸，彼此分开（图3）。为了进一步验证立体化学分配，对围绕C10-C11和C11-C12轴的旋转异构体采用基于J的构型分析7。通过J-HMBC实验测得H10/C11和H12/C11的异源长程偶合常数2JCH分别为5.6Hz和2.3Hz。8这些值建立了H10和11-OH的gauche关系以及H12和11-OH的anti关系（图4），与NOESY实验和基于3JHH偶联值的构型分析的结果一致。根据这些光谱证据，确定了1中存在的不对称中心具有10R，11R和12S构型。这些立体化学信息将有助于评价1作为免疫抑制或抗糖尿病药物的主要支架的构效关系研究。
NFAT-133 (1) is a relatively small, aromatic polyketide isolated from actinomycete strains of the genera Dactylosporangium 1 and Streptomyces (Figure 1). 2 This trialkyl-substituted benzene derivative bears three contiguous stereocenters comprising hydroxy and methyl substitutions on an alkyl side chain but the relative and absolute configurations remain unknown. NFAT-133 (1) is a pharmaceutically interesting molecule with immunosuppressive and antidiabetic activity. It inhibits transcription mediated by NFAT (nuclear factor of activated T cells), leading to the suppression of IL-2 (interleukin-2) expression and the following T cell proliferation. 1 In addition, this compound stimulates glucose uptake in skeletal muscle cells. In vivo experiments with db/db mice demonstrated its efficacy of lowering plasma glucose and insulin, without body weight gaining, 2 which is a side effect of currently used thiazolidine-class antidiabetic drugs (In Kulkarni-Almeida et al., 2 the structure of NFAT-133 is incorrectly presented with respect to the C2/C3 double bond). In order to explore the biological potency of chemically modified derivatives of NFAT-133 (1), it became necessary to assign its absolute configuration. In our ongoing program on chemical investigation of secondary metabolite diversity in Streptomyces species, 3–5 production of 1 was noticed in the culture extract of Streptomyces karnatakensis NBRC 13051. This strain was grown in liquid medium and several steps of purification from the culture extract afforded 1 in a pure form. 1H and 13C NMR spectral data of 1 from strain NBRC 13051 were identical with those previously reported for NFAT-133 (Table 1). 1, 2 Stereochemical analysis was started with the application of chiral anisotropy method 6 to the secondary hydroxy group at C11. Esterification of 1 by treatment with (S)-and (R)-MTPACl gave bis-(R)-and (S)-MTPA esters (2a and 2b), respectively. The ΔδS-R values were calculated by subtracting the 1H NMR chemical shifts δH of 2a from that of 2b. Although the ΔδS-R values were zero for H12 and H17, a positive value was observed for H14 and negative values were observed for H2, H3, H10 and H16. 6 The absolute configuration at C11 was thus determined as R. The relative configuration at C10 and C12 was deduced from the analysis of the coupling constants. The large 3JH10, H11 (7.0 Hz) and the small 3JH11, H12 values (3.9 Hz) indicated the anti and syn relationships for H10/H11 and H11/H12, respectively (Figure 2). This assignment was in good agreement with the NOEs observed between H10 and H17 and between H12 and H16 in the NOESY spectrum (Figure 3). Furthermore, NOEs between H3 and H10, H8 and H11, and H2 and H5 suggested that the side chains at C4 and C9 were extending from the aromatic core to set apart from each other (Figure 3). To further validate the stereochemical assignment, J-based configuration analysis 7 was employed for the rotamers around C10–C11 and C11–C12 axes. Heteronuclear long-range coupling constants 2JCH were determined to be 5.6 Hz for H10/C11 and 2.3 Hz for H12/C11 by J-HMBC experiment. 8 These values established the gauche relationship for H10 and 11-OH and the anti relationship for H12 and 11-OH (Figure 4), consistent with the results from the NOESY experiment and configuration analysis based on 3JHH coupling values. On the basis of these spectroscopic evidences, the asymmetric centers present in 1 were determined to have 10R, 11R and 12S configurations. This stereochemical information will facilitate the structure-activity relationship study for evaluation of 1 as a lead scaffold for the immunosuppressive or antidiabetic …