Browsing by Author "Li, Wei"

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    Intrapersonal day-to-day travel variability and duration of household travel surveys: Moving beyond the one-day convention
    (Journal of Transport and Land Use, 2018) Li, Wei; Houston, Douglas; Boarnet, Marlon G.; Park, Han
    By analyzing seven-day travel logs from Los Angeles during 2011–2013, we contribute to the understanding of intrapersonal day-to-day travel variability (IDTV) in relation to socio-demographic and land-use characteristics and the implication of travel survey duration for travel parameter estimates. Our main sample included 2,395 person-days from 352 individual participants in 219 households. Our analytical methods included linear regressions and random sampling experiments. Our Feasible Generalized Least Squares (FGLS) regression models revealed that many factors significantly influenced IDTV, such as gender, age, income, and household type. However, the observed socio-demographic and land-use characteristics could only explain a small portion of IDTV. The random sampling experiments enabled us to contrast travel variables measured from the seven-day master sample with those from subsamples of a shorter period (one to six days). The “optimal” duration for a travel survey may depend on the specific travel variables measured, and we provide evidence that studies of transit and non-motorized travel will require longer surveys than studies of car travel. In conclusion, the conventional one-day approach is likely to produce imprecise parameter estimates due to the intrapersonal day-to-day travel variability. We recommend that transportation professionals and policy makers consider shifting from the conventional one-day approach toward a multi-day approach. Surveys that focus on the modes of walking, biking, and transit should consider data collection for at least seven days.
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    Macrocyclization Through Ene-Yne Cross-Coupling/Alkyne Reduction Tandem Reaction And Its Application In Natural Product Synthesis
    (2015-09) Li, Wei
    Chapter 1 — Macrocyclization Through Copper-Catalyzed Castro–Stephens Coupling/Alkyne Reduction Tandem Reaction Macrocycles, incorporating conjugated polyene subunits within the ring, are structural features found in a number of natural products that exhibit diverse and potent biological activities. Existing methods for the construction of such structures are limited and in many cases inefficient. We discovered an unprecedented copper-mediated reductive ene–yne macrocyclization reaction during our pursuit of the total synthesis of oximidine II. The reaction selectively generates an endocyclic Z-double bond through an intramolecular coupling of a vinyl iodide and a terminal alkyne fragment followed by in situ alkyne reduction. We developed this transformation as a general method for the preparation of polyunsaturated macrocycles. The reaction conditions were optimized and the scope of the reaction was extensively explored. It was found that the alkyne reduction step is driven by the release of the ring strain. Thus, the reaction is particularly efficient for suitably strained 11- to 13-membered E,Z-1,3-diene macrocycles. A complementary stepwise procedure was employed for the synthesis of larger rings. Finally, a plausible reaction mechanism was proposed based on experimental findings. HASH(0x7f87dd8493f8) Chapter 2 — Formal Total Synthesis of Lactimidomycin Lactimidomycin is a macrocyclic natural product that possesses potent in vitro and in vivo anti-tumor activities. We accomplished a facile, 9-step synthesis of an advanced intermediate for the total synthesis of lactimidomycin. The crucial 12-membered polyene lactone core structure was constructed employing our newly developed Castro–Stephens coupling/alkyne reduction tandem reaction. The stereocenters were established via asymmetric a vinylogous aldol reaction and a Marshall’s propargylation reaction. Chapter 3 — Synthesis and Biological Evaluation of Oximidine II Analogues Oximidine II belongs to a family of benzolactone enamide natural products that exert their cytotoxic effects through inhibition of V-ATPases. Unlike other members of this family, the structure-activity relationship (SAR) of oximidines has not been extensively investigated. Guided by computational analysis and previous studies in our group, we designed and synthesized two oximidine II analogues with simplified scaffold. The simplified benzolactone core was accessed through a ring-closing metathesis (RCM) reaction and the enamide side chain was installed via a copper-mediated C–N coupling reaction. The analogues were evaluated for their biological activity. The results revealed that these molecules were weakly cytotoxic to a number of cancer cell lines.