Xing-Ren Li

Broadly Tunable Dual-Wavelength Erbium-Doped Ring Fiber Laser Based on a High-birefringence Fiber Loop Mirror

A broadly tunable dual-wavelength erbium-doped ring fiber laser based on a high-birefringence fiber loop mirror (HiBi-FLM) and a polarization controller is demonstrated experimentally. The measured transmission spectrum of HiBi-FLM covers a wide range from 1525 to 1575 nm. The wavelength of proposed laser can be flexibly tunable during this range of ∼50 nm by adjusting the polarization controller. In addition, the spacing of two wavelengths is adjustable by changing the length of HiBi fiber. The dual-wavelength lasers with the HiBi fiber length of 1 and 2 m are experimentally demonstrated and compared. The experimental results show that the proposed laser can stably operate on two wavelengths simultaneously at room temperature, and the output peak power variation is about 0.5 dB during 40 min.

All-normal dispersion, figure-eight, tunable passively mode-locked fiber laser with an invisible and changeable intracavity bandpass filter

We report dissipative solitons generation in the figure-8 all-normal dispersion fiber ring laser. The steep edge of the output optical spectrum results from the filtering effect of NOLM together with polarization controllers (PCs). No any physical bandpass filters are used in the cavity. Moreover, the output wavelength can be tuned in a wide range of about 20 nm. In the long-wavelength region, the spectral filtering effect of NOLM becomes weaker and output spectrum shows only one steep side. Filtering effect can perform periodically with increasing the pump power. The highly chirped pulse has good potential for application to the chirped pulse amplification (CPA) system.

Scopariusicides, Novel Unsymmetrical Cyclobutanes: Structural Elucidation and Concise Synthesis by a Combination of Intermolecular [2 + 2] Cycloaddition and C–H Functionalization

Scopariusicides A (1) and B (2), two novel immunosuppressive unsymmetrical cyclobutane derivatives, were isolated from the aerial parts of Isodon scoparius. Moreover, based on the results of phytochemical investigation, a concise stereocontrolled synthesis of scopariusicide A and its analogues with enhanced biological activities was efficiently achieved using the main diterpenoid (3) isolated from this plant as a readily available starting material. A crossed intermolecular [2 + 2] photocycloaddition and a Pd-catalyzed sp(3) C-H bond β-arylation were used synergistically to access the highly congested unsymmetrical cyclobutane core with four contiguous stereocenters.

Spacing-tunable multi-wavelength fiber laser based on cascaded four-wave mixing in highly nonlinear photonic-crystal fiber

A multi-wavelength fiber laser based on the cascaded four-wave mixing in highly-nonlinear photonic-crystal fiber is proposed and investigated. The cascade operation is initiated by two strong pump waves boosted by multi-mode pumping erbium/ytterbium co-doped double-cladding fiber amplification technique. A segment of highly-nonlinear near-zero-dispersion-flattened photonic crystal fiber is employed to induce highly efficient cascaded four-wave mixing. The wavelength spacing can be continuously tunable by stretching the fiber Bragg grating. Experimental results show that multiple wavelengths with a high optical side-mode suppression-ratio of >30 dB are achieved. Furthermore, the proposed multi-wavelength fiber laser exhibits an excellent stability at room temperature.

Low-repetition-rate ytterbium-doped fiber laser based on a CFBG from large anomalous to large normal dispersion

We report on the long-cavity ytterbium-doped fiber laser based on a chirped fiber Bragg grating (CFBG) to control the dispersion in the cavity. The proposed fiber lasers operating in large anomalous dispersion and large normal dispersion are intensively studied in this paper. To the best of our knowledge, this is the first time for us to give the dispersion map over such a wide range. The experimental results show that, for large anomalous dispersion, the state of soliton rains can be obtained. Nanosecond pulse is obtained in the large normal dispersion regime with spectral filter which is different from the operation mode without spectral filter. This study may pave the way to best apply the fiber laser in many fields.

Structurally Diverse Diterpenoids from Isodon scoparius and Their Bioactivity

Fourteen new diterpenoids (1-14) based on four skeletal types and two known analogues (15 and 16) were isolated from the aerial parts of Isodon scoparius. Compound 2 is the first ent-kaurane diterpenoid featuring a 1,11-ether bridge, and the structures of these new compounds were established mainly by NMR and MS methods. The absolute configurations of 1 and 5 and the relative configuration of 3 were determined using single-crystal X-ray diffraction. The absolute configuration of 14 was determined by comparison of the experimental and calculated electronic circular dichroism spectra. Compounds 1, 4, and 15 were active against five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480), and they also inhibited NO production in LPS-stimulated RAW264.7 cells, with IC50 values of 1.0, 3.1, and 1.8 μM, respectively.

Ent-Abietanoids Isolated from Isodon serra

Four new ent-abietane diterpenoids, along with four known ones were isolated from the aerial parts of Isodon serra, a traditional Chinese folk medicine. The new diterpenoids were named as serrin K (1), xerophilusin XVII (2), and enanderianins Q and R (3 and 4), while the known ones were identified as rubescansin J (5), (3α,14β)-3,18-[(1-methylethane-1,1-diyl)dioxy]-ent-abieta-7,15(17)-diene-14,16-diol (6), xerophilusin XIV (7), and enanderianin P (8), respectively. Their structures were elucidated by extensive spectroscopic analysis and comparison with the literature. Compound 1 showed remarkable inhibitory activity towards NO production in LPS-stimulated RAW264.7 cells (IC50 = 1.8 μM) and weak cytotoxicity towards five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480).

7α,20-Epoxy-ent-kaurane Diterpenoids from the Aerial Parts of Isodon pharicus

A phytochemical investigation of an ethyl acetate extract of the aerial parts of Isodon pharicus led to the isolation of 21 new 7α,20-epoxy-ent-kaurane diterpenoids, pharicins C-W (1-21), and 29 known (22-50) analogues. The structural characterization of 1-21 and assignment of their relative configurations were accomplished by spectroscopic data interpretation, while the structures of 1 and 16 were confirmed by X-ray crystallography. The absolute stereostructure of 1 was confirmed by electronic circular dichroism data analysis. Twenty-five of the diterpenoids were screened for their cytotoxic activities against a panel of tumor cell lines, including HL-60, SMMC-7721, A-549, MCF-7, and SW-480. Compounds 11, 16, 38, and 48 exhibited inhibitory activities against these tumor cell lines with IC50 values ranging from 1.01 to 9.62 μM, while 2, 15, 29, and 47 exhibited moderate cytotoxic potency.

Structurally diverse diterpenoids from Isodon pharicus

Twenty-one diterpenoids with diverse structures, including twelve new compounds (1–12), were isolated from the aerial parts of Isodon pharicus. Structurally, pharicusin A (1), composed of a benzoyl group coupled to a 7α,20-epoxy-ent-kauranoid, represents an unprecedented C27 meroditerpenoid; pharicusin B (2) is a novel trinorditerpenoid with an unreported 15,16,17-trinor-7α,20-epoxy-ent-kaurane skeleton; pharicusin C (4) represents the first example of 7α,20-epoxy-ent-atisane diterpenoids. Their structures were elucidated based on spectroscopic analysis, wherein the absolute configurations of 2 and 3 were further confirmed by single-crystal X-ray diffraction and computational analysis of the optical rotatory dispersion (ORD). Selected sixteen isolates were evaluated for their in vitro cytotoxicity against a small panel of human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480), and compounds 9, 10, 13, 16, and 18 exhibited significant inhibitory effects against all five cell lines, with IC50 values in the range of 0.37–6.03 μM.

Isoscoparins R and S, two new ent-clerodane diterpenoids from Isodon scoparius

Abstract Two new ent-clerodane diterpenoids, named isoscoparins R and S (1 and 2), were isolated from the aerial parts of Isodon scoparius. Their structures were characterized mainly by analyzing the NMR and HRESIMS data, and the relative configuration of compound 1 was determined by single-crystal X-ray diffraction. Compound 2 showed weak activity as an autophagic inhibitor.