Application of Residual Dipolar Couplings and Selective Quantitative NOE to Establish the Structures of Tetranortriterpenoids from <i>Xylocarpus rumphii</i>

Nine triterpenoid derivatives were isolated from the heartwood of <i>Xylocarpus rumphii</i> and were identified as xylorumphiins E (<b>1</b>), C (<b>2</b>), L (<b>3</b>), and M–R (<b>4</b>–<b>9</b>). Compounds <b>4</b>–<b>9</b> have a hemiacetal group in the triterpenoid side chain, making them impossible to purify. Purification was achieved after acetylation and subsequent separation of the epimeric mixtures of acetates; however differentiaition of the <i>R</i> and <i>S</i> epimers was not possible using standard NMR techniques. In one case, the relative configuration of a remotely located stereocenter with respect to the stereocenters in the main skeleton was unambiguously determined using residual dipolar couplings. Dipolar couplings were collected from the sample oriented in compressed poly­(methyl methacrylate) gels swollen in CDCl₃. In another case, the relative configuration was determined using 1D selective quantitative NOE experiments. Xylorumphiin K (<b>10</b>), xyloccensin E, taraxer-14-en-3β-ol, (22<i>S</i>)-hydroxytirucalla-7,24-diene-3,23-dione, and 25-hydroxy-(20<i>S</i>,24<i>S</i>)-epoxydammaran-3-one were isolated from the bark of the same plant. Compounds <b>3</b>–<b>10</b> are new compounds. Compounds <b>1</b>–<b>6</b> and xyloccensin E were tested at one concentration, 1 × 10^–5 M, in the NCI59 cell one-dose screen but did not show significant activity

Application of Residual Dipolar Couplings and Selective Quantitative NOE to Establish the Structures of Tetranortriterpenoids from <i>Xylocarpus rumphii</i>

Nine triterpenoid derivatives were isolated from the heartwood of <i>Xylocarpus rumphii</i> and were identified as xylorumphiins E (<b>1</b>), C (<b>2</b>), L (<b>3</b>), and M–R (<b>4</b>–<b>9</b>). Compounds <b>4</b>–<b>9</b> have a hemiacetal group in the triterpenoid side chain, making them impossible to purify. Purification was achieved after acetylation and subsequent separation of the epimeric mixtures of acetates; however differentiaition of the <i>R</i> and <i>S</i> epimers was not possible using standard NMR techniques. In one case, the relative configuration of a remotely located stereocenter with respect to the stereocenters in the main skeleton was unambiguously determined using residual dipolar couplings. Dipolar couplings were collected from the sample oriented in compressed poly­(methyl methacrylate) gels swollen in CDCl₃. In another case, the relative configuration was determined using 1D selective quantitative NOE experiments. Xylorumphiin K (<b>10</b>), xyloccensin E, taraxer-14-en-3β-ol, (22<i>S</i>)-hydroxytirucalla-7,24-diene-3,23-dione, and 25-hydroxy-(20<i>S</i>,24<i>S</i>)-epoxydammaran-3-one were isolated from the bark of the same plant. Compounds <b>3</b>–<b>10</b> are new compounds. Compounds <b>1</b>–<b>6</b> and xyloccensin E were tested at one concentration, 1 × 10^–5 M, in the NCI59 cell one-dose screen but did not show significant activity

Application of Residual Dipolar Couplings and Selective Quantitative NOE to Establish the Structures of Tetranortriterpenoids from <i>Xylocarpus rumphii</i>

Nine triterpenoid derivatives were isolated from the heartwood of <i>Xylocarpus rumphii</i> and were identified as xylorumphiins E (<b>1</b>), C (<b>2</b>), L (<b>3</b>), and M–R (<b>4</b>–<b>9</b>). Compounds <b>4</b>–<b>9</b> have a hemiacetal group in the triterpenoid side chain, making them impossible to purify. Purification was achieved after acetylation and subsequent separation of the epimeric mixtures of acetates; however differentiaition of the <i>R</i> and <i>S</i> epimers was not possible using standard NMR techniques. In one case, the relative configuration of a remotely located stereocenter with respect to the stereocenters in the main skeleton was unambiguously determined using residual dipolar couplings. Dipolar couplings were collected from the sample oriented in compressed poly­(methyl methacrylate) gels swollen in CDCl₃. In another case, the relative configuration was determined using 1D selective quantitative NOE experiments. Xylorumphiin K (<b>10</b>), xyloccensin E, taraxer-14-en-3β-ol, (22<i>S</i>)-hydroxytirucalla-7,24-diene-3,23-dione, and 25-hydroxy-(20<i>S</i>,24<i>S</i>)-epoxydammaran-3-one were isolated from the bark of the same plant. Compounds <b>3</b>–<b>10</b> are new compounds. Compounds <b>1</b>–<b>6</b> and xyloccensin E were tested at one concentration, 1 × 10^–5 M, in the NCI59 cell one-dose screen but did not show significant activity

Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

The synthesis and functionalization of the parent 1,3-benzothiaphosphole is reported. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metalation of the 2-position using lithium diisopropylamide proceeded smoothly according to ³¹P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. The PC bond of the thiaphosphole was also explored as a dienophile in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures were fully characterized, and a solid-state molecular structure of the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar coupling (RDC) NMR experiments were used to assign major and minor products for the isoprene and cyclopentadiene adducts

Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

The synthesis and functionalization of the parent 1,3-benzothiaphosphole is reported. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metalation of the 2-position using lithium diisopropylamide proceeded smoothly according to ³¹P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. The PC bond of the thiaphosphole was also explored as a dienophile in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures were fully characterized, and a solid-state molecular structure of the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar coupling (RDC) NMR experiments were used to assign major and minor products for the isoprene and cyclopentadiene adducts

Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

The synthesis and functionalization of the parent 1,3-benzothiaphosphole is reported. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metalation of the 2-position using lithium diisopropylamide proceeded smoothly according to ³¹P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. The PC bond of the thiaphosphole was also explored as a dienophile in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures were fully characterized, and a solid-state molecular structure of the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar coupling (RDC) NMR experiments were used to assign major and minor products for the isoprene and cyclopentadiene adducts