Lam-Lung Yeung
Hong Kong University of Science and Technology
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Featured researches published by Lam-Lung Yeung.
Tetrahedron Letters | 1993
Geert-Jan Boons; Peter Grice; Ray Leslie; Steven V. Ley; Lam-Lung Yeung
The reactivity of dispiroketal protected thioglycosides makes them useful new precursors for oligossaccharide synthesis as is illustrated by the preparation of a protected pentasaccharide unit common to the variant surface glycoprotein of Trypanosoma brucei.
Journal of The Air & Waste Management Association | 2006
Steven Sai Hang Ho; Jian Zhen Yu; Kam Wah Chu; Lam-Lung Yeung
Abstract Cooking fumes are an important carbonyl emission source, especially in a highly urbanized city, such as Hong Kong. Cooking exhaust from 15 commercial kitchens of a variety of cooking styles was sampled and analyzed for a suite of 13 carbonyl compounds. Carbonyl compositions were varied among the different cooking styles. Formal dehyde was generally the most abundant carbonyl, and its contribution to the total carbonyl amount on a molar basis ranged from 12 to 60%. Acrolein was also found to be an abundant carbonyl in the cooking exhaust. The highest contribution by acrolein to the total carbonyls was found to be 30% in the exhaust of a western-style steak restaurant. Long-chain saturated carbonyls, that is, heptanal, octanal, and nonanal, accounted for a signifi-cant fraction (>40%) of the total carbonyls in kitchens that always used heated cooking oils. Two dicarbonyls, glyoxal and methylglyoxal, had a various presence in the cooking emissions, ranging from negligible to 10%. The presence of benzaldehyde and tolualdehyde was mostly negligible in the sampled kitchen exhaust. Annual emission rates of both individual carbonyls and total carbon-yls were estimated for various types of commercial kitchens. Local-style fast-food shops contributed the highest total carbonyl emissions per year mainly because of the large number of this kind of restaurant in Hong Kong. The citywide annual emission rates of the three most toxic carbonyls, formaldehyde, acetaldehyde, and acrolein, were estimated assuming that the limited number of sampled restaurants were representative of the average restaurants. Such estimates of carbonyl emission rates were comparable to the estimated carbonyl emissions from vehicular sources, suggesting the importance of commercial cooking as a source for carbonyls in Hong Kong.
European Journal of Organic Chemistry | 2000
Richard K. Haynes; Tin-Lok Au-Yeung; Wai-Kuen Chan; Wai-Lun Lam; Zhi-Yi Li; Lam-Lung Yeung; Albert S. C. Chan; Pauline Li; Mark Koen; Craig R. Mitchell; Simone Charlotte Vonwiller
P-Chiral tertiary phosphane oxides have been prepared from each of the secondary phosphane oxides racemic 1, (SP)-(−)-4 and (RP)-(+)-tert-butylphenylphosphane oxide (5) by lithiation with LDA or nBuLi, or sodiation with sodium hydride, in THF, and then by treatment with a series of primary alkyl halides. Doubly P-chiral ditertiary bis(phosphane oxides) are also obtained from these metallated secondary phosphane oxides by treatment with electrophiles based on straight-chain, tartrate-derived, and bishalomethylarene dihalides. In general, the bis-phosphane oxides are obtained in good yields. However, when the α,ω-dihalide bears an embedded heteroatom (O or Si), yields are diminished. The enantiomeric purity of each of the products was assessed through admixture with (RP)- and (SP)-tert-butyl(phenyl)phosphanylthioic acids and measurement of the tert-butyl resonances in the 1H-NMR spectra. In all cases, the act of metallation of the enantiomerically pure secondary phosphane oxide followed by its alkylation is not accompanied by detectable racemization. This method for preparing P-chiral tertiary phosphane oxides is therefore more straightforward than those described previously.
Tetrahedron Letters | 1996
Richard K. Haynes; William Wai‐Lun Lam; Lam-Lung Yeung
Abstract Nucleophilic carbonyl and conjugate addition reactions of configurationally stable lithiated P-chiral tert-butylphenylphosphine oxide with aldehydes and α,β-unsaturated carbonyl compounds occur in good yields with diastereoselectivities ranging from 33 to ≥98 %.
Journal of Biomedical Science | 2003
Nai-Ki Mak; Tsz-Wai Kok; Ricky Ngok-Shun Wong; Sum-Wai Lam; Yan-Kin Lau; Wing-Nang Leung; N. H. Cheung; Dolly P. Huang; Lam-Lung Yeung; C. K. Chang
Two sulfonamide derivatives of porphycene, namely PS6 and PS6A, were synthesized, and their photodynamic efficacies on the nasopharyngeal carcinoma (NPC) cell line NPC/CNE-2 were evaluated. By comparing the 50% lethal concentrations (LC(50)) of these photosensitizers, we found that PS6A with a cationic ammonium group on the side chain exhibited potent photocytotoxicity on the NPC cell line. At a light dose of 1 J/cm(2), the LC(50) values of PS6 and PS6A for NPC cells were 11.6 and 1.92 microM, respectively. CNE-2 was found to rapidly take up PS6A in the first hour of incubation, and the uptake kinetics steadily increased to a plateau level after 18 h of incubation. The uptake of PS6A was temperature dependent. Over 99% of CNE-2 cells were sensitized by PS6A 24 h after drug treatment. Collapse of the mitochondrial membrane potential was also observed in PS6A photodynamic therapy (PDT)-treated CNE-2 cells 1.5 h after PDT. Confocal microscopy revealed that PS6A was predominantly localized in the mitochondria, lysosomes and Golgi bodies of NPC cells. Significant genotoxicity was not observed in CNE-2 cells. In functional studies, the in vitro formation of a capillary-like network of human umbilical vein endothelial cells in Matrigel was greatly inhibited by PS6A PDT in a dose-dependent manner. In conclusion, PS6A mediates both in vitro antitumor and antiangiogenic activities. PS6A might be a candidate for photodynamic treatment of NPCs.
Tetrahedron Letters | 1996
Wa-Hung Leung; Man T. Yu; Man Ching Wu; Lam-Lung Yeung
Cr(NBut)Cl3(dme) catalyzes ring-opening of N-tosylaziridines with trimethylsilyl azide; the yield and selectivity of which was found to be enhanced by molecular sieves.
Indoor and Built Environment | 2008
Lam-Lung Yeung; W.M. To
Exposure to cooking fumes may be responsible for respiratory health effects. However, the linkage between such exposures and these effects cannot be established without knowing the size distribution of the aerosols emitted from cooking activities. This study examined the size distribution of the aerosols generated by commercial cooking processes. It was found that the aerosol size distributions were lognormal. Several theoretical models can explain the lognormal characteristic of aerosols from cooking processes and the simplest one is a bounded multiplicative process that represents the growth (or shrinkage) of aerosols in a random manner. Our results showed that by defining the mode diameter (geometric mean diameter) and the dimensionless geometric standard deviation one could describe the size distribution of cooking fumes in general. This characterization model can be applied to cooking fumes from indoor as well as outdoor cooking processes. The results of our measurement also showed that the mode diameter of aerosols increased when cooking temperature increased. The normalized number concentration of sub-micrometer aerosols increased rapidly when cooking temperature increased especially in the size range between 0.1 and 1.0 μm, known as the accumulation mode.
Tetrahedron Letters | 2001
Tin-Lok Au-Yeung; Ka-Yee Chan; Wai-Kuen Chan; Richard K. Haynes; Ian D. Williams; Lam-Lung Yeung
Reaction of ( R P )- and ( S P )- tert -butylphenylphosphinobromidates and tert -butylphenylthionophosphinochloridates with metallated phenol and BINOL alkoxides, thioalkoxides, amides and enolates leading with clean inversion at phosphorus to phosphinates, phosphinothiolates and phosphinoamidates, and the corresponding thionophosphorus compounds are described.
Tetrahedron Letters | 1995
Wa-Hung Leung; Ernest Kin-Fai Chow; Man-Ching Wu; Polly W.Y. Kum; Lam-Lung Yeung
Abstract Organoimido complexes of Group-VI transition metals were found to catalyze ring-opening of epoxides by trimethylsilyl azide and amines with good regioselectivities.
PLOS ONE | 2013
Leo Lap-Yan Wong; Ian Pak-Yan Lam; Tracy Yuk-Nar Wong; Wai-Lung Lai; Heong-Fai Liu; Lam-Lung Yeung; Yick-Pang Ching
Hepatocellular carcinoma (HCC) is one of the major malignancies worldwide and is associated with poor prognosis due to the high incidences of metastasis and tumor recurrence. Our previous study showed that overexpression of p21-activated protein kinase 1 (PAK1) is frequently observed in HCC and is associated with a more aggressive tumor behavior, suggesting that PAK1 is a potential therapeutic target in HCC. In the current study, an allosteric small molecule PAK1 inhibitor, IPA-3, was evaluated for the potential in suppressing hepatocarcinogenesis. Consistent with other reports, inhibition of PAK1 activity was observed in several human HCC cell lines treated with various dosages of IPA-3. Using cell proliferation, colony formation and BrdU incorporation assays, we demonstrated that IPA-3 treatment significantly inhibited the growth of HCC cells. The mechanisms through which IPA-3 treatment suppresses HCC cell growth are enhancement of apoptosis and blockage of activation of NF-κB. Furthermore, our data suggested that IPA-3 not only inhibits the HCC cell growth, but also suppresses the metastatic potential of HCC cells. Nude mouse xenograft assay demonstrated that IPA-3 treatment significantly reduced the tumor growth rate and decreased tumor volume, indicating that IPA-3 can suppress the in vivo tumor growth of HCC cells. Taken together, our demonstration of the potential preclinical efficacy of IPA-3 in HCC provides the rationale for cancer therapy.