Structure of the tetranortriterpene bussein

Abstract

Bussein is shown to be a mixture of bussein A, C44H56018, and bussein B, C,,H,O,, ; structure (Ia) is proposed for bussein A and structure (Ib) for bussein B.caudatum Sprague,l and has been concluded to contain, among others, three acetyl, one isobutyryl, and one 2-methylbutyryl g r o u ~s . ~, ~We have found that bussein is a mixture of two components, i.e. bussein A, C,H,,O,,, and bussein B, C4,HM01,, to which structures (Ia) and (Ib), respectively, are assigned. The mass spectrum of a crystalline sample, BUSSEIN is a crystalline compound isolated from the timber of Entandrophragma bussei Harms. and Entandrophragma 1964, 322.

Spin‐orbit ZORA and four‐component Dirac–Coulomb estimation of relativistic corrections to isotropic nuclear shieldings and chemical shifts of noble gas dimers

“…We are only aware of one earlier calculation of vibrational corrections to noble gas dimer chemical shifts, a CCSD calculation on Xe 2 . [24] Their averaged CCSD value for the dimer shift, 29.93 ppm, is in very good agreement with our value 30.30 ppm.…”

“…Comparison of our CCSD(T) results with literature values [12,16,21,[23][24][25][26] obtained at the CCSD or higher levels but with different one-electron basis sets and sometimes at slightly different equilibrium geometries shows excellent agreement.…”

“…[11][12][13][14][15][16][17][18] Besides, the chemical shift of the lighter dimers He 2 , Ne 2 , Ar 2 , and of Xe 2 were also predicted using nonrelativis-tic, but high-level correlated wavefunction methods. [19][20][21][22][23][24][25][26] However, systematic studies on the heavier Ng dimers with inclusion of relativistic terms are lacking apart from Xe 2 . [18] Due to its favorable cost-to-performance ratio, density functional theory (DFT) or Hartree-Fock (HF) will be the method of choice for calculations on noble gases interacting with large molecular systems such as nanomaterials.…”

Twelve Novel and Diverse 16-Norphragmalin-Type Limonoids from Chukrasia tabularis var. velutina

“…The C-15-acyl 16-norphragmalins isolated in this investigation and reported previously [11][12][13][14] could be correlated well by the plausible biosynthetic pathway, and we think that the origin of carbonate moiety in 16-norphragmalin limonoids (1)(2)(3)(4)(5)(6)(7)(8) maybe comes from the 16-carbonyl of phragmalin skeleton which degradated through decarboxylation. Herein, the isolation, structural elucidation, the anti-inflammatory activity, as well as the proposed biosynthetic pathway of these novel compounds were reported.…”

129Xe NMR chemical shift in Xe@C60 calculated at experimental conditions: Essential role of the relativity, dynamics, and explicit solvent

“…Numerous computational studies on 129 Xe NMR properties have been reported for molecules containing Xe [30][31][32][33][34][35] as well as for Xe atom guest-host systems. [33,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] In this article, we study the 129 Xe CS of endohedral Xe atom in Xe@C 60 molecule with particular aim at faithful simulations of experimental conditions and assessment of the different physical contributions to the experimental 129 Xe NMR CS, such as relativistic, dynamic, and solvent effects.…”