Asu Usta
Karadeniz Technical University
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Publication
Featured researches published by Asu Usta.
Journal of Asian Natural Products Research | 2005
Nuri Yildirim; N. Doğan; Asu Usta; L. Altun
One new triterpene compound, 3β-acetoxylup-20(30)-en-29-al (1) and two known 3-acetylptiloepoxide (2) and 3β-acetoxylup-20(29)-ene (3) were isolated for the first time from the leaves of Campanula lactiflora and their structures were deduced by high field 1D and 2D 400 MHz NMR, EI-MS and (+) LC-MS/MS spectra.
Journal of Molecular Modeling | 2010
Ahmet Yaşar; Nuran Yaylı; Asu Usta
Photodimerization reactions of compounds 4–6 gave four new cyclobutane-containing compounds (7–9) with full control over the stereochemistry at the four stereogenic centers. These new cyclobutane-containing compounds had β-truxinic (7a), δ-truxinic (7b and 9), and ε-truxillic (8) structures. However, o-, m-, and p-hydroxy 4-azachalcones (1–3) did not give photochemical cyclization products under any conditions (in solvent or in their solid or molten states). Experimental data suggested the possibility of frontier orbital control over stereochemical behavior, so some theoretical calculations were performed. Full geometrical optimization of compounds 1–9 was performed via DFT B3LYP/6-31+G**, and their electronic structures were also investigated. The geometries of the singlet and triplet states were initially optimized by density functional theory (DFT) and the configuration interaction singles (CIS) B3LYP/3-21+G** level. An additional calculation was performed for the triplet state using the ground-state geometry. The possible photochemical dimerization products of compounds 7–9 (a–g) and the intrinsic reaction coordinates (IRCs) of the reactions of compounds 4–6 were calculated theoretically by the DFT/3-21+G** method. The configurations (reactant, transition state, product, and reaction pathway) corresponding to the stationary points (minima or saddle points) were determined. The intrinsic reaction coordinates were followed to verify the energy profiles that connect each TS to the appropriate local minimum. The dimeric products expected from the calculations coincided with the dimers produced experimentally.
Phytochemistry | 2005
Ahmet Yaşar; Canan Güleç; Asu Usta; Sevgi Kolayli; Kamil Coşkunçelebi; Şengül Alpay Karaoğlu
Turkish Journal of Chemistry | 2003
Nuri Yildirim; Asu Usta
Helvetica Chimica Acta | 2007
Asu Usta; Ahmet Yaşar; Nagihan Yılmaz; Canan Güleç; Nuran Yaylı; Şengül Alpay Karaoğlu
Asian Journal of Chemistry | 2009
Asu Usta; O. Üçüncü; Tayyibe Beyza Cansu; Salih Terzioğlu
Journal of Applied Polymer Science | 2006
Dilek Kul; Sevil Savaskan Yilmaz; Temel Öztürk; Asu Usta; Murat Misir
Asian Journal of Chemistry | 2010
Nuran Kahriman; Canan Albay; N. Doğan; Asu Usta; Sengul Alpay Karaoglu
Turkish Journal of Chemistry | 2009
Asu Usta; Ahmet Yaşar; Nuran Yaylı; Şengül Alpay Karaoğlu
Turkish Journal of Chemistry | 2006
Asu Usta; Ahmet Yaşar; Osman Üçüncü; Canan Güleç; Mustafa Küçükislamoğlu