Download Information Regarding Prof

Information Regarding Prof. Loh T. P.’s Publications
The following information is collated for personal use in order to understand the research
projects under Prof. Loh’s charge. The following information includes the summary of
each of his research papers and should not be circulated without his express permission.
Basically, the research projects currently under his charge can be subdivided into four
categories:
- Enantioselective reactions
- Development of new synthetic methodology
- Green Chemistry
- Total synthesis of natural products
1) Product Class 3: Indium Compounds
Abstract:
A report which mentions the methods for the synthesis of indium compounds like allylic
indium complexes, propargylic/ allenylic indium complexes, Reformatsky-type indium
complexes, indium carbenoids, alkylindium (III) complexes, tetraorganoindates,
indium(III) trifluoromethanesulfonate. This report also includes application to organic
synthesis.
2) Synthetic Studies toward Kaitocephalin
Abstract:
To synthesize a general methodol to gain access to 32 potential stereoisomers, synthetic
studies towards total synthesis of kaitocephalin was carried out at the time of
commencement. This results in an interesting and unexpected result being observed in the
highly anticipated stereoselective key aldol reaction.
3) Progress towards the total synthesis of tedanolide: an efficient assembly of the
C1-C11 subunit
Abstract:
TBS O
Me
Me
Me
Me
O TBDPS
tBuO
2C
OMe
O
O
Me
Me
I
The C1-C11 subunit (I) of tedanolide was constructed via a boron-mediated synthetic
aldol reaction as key step to control C6 and C7 stereocenters. Also, asymmetric sharpless
dihydroxylation includes the C2, C3 hydroxyl groups, protects the hydroxyl group at C2
and uses a tert. butyl ester to withstand the attack of Grignard and enolate reagents.
4) InCl3-Catalyzed direct aldol reactions of glyoxylic acid monohydrate and
glyoxylates with various ketones: scope and limitations.
Abstract:
The direct aldol reactions of a variety of ketones with glyoxylic acid and glyoxylates
result in good yields and high regioselectivities for -hydroxy acid and -hydroxy esters.
5) Concise synthesis of ()-methylenolactocin and the formal synthesis of ()phaseolinic acid
Abstract:
()-Methylenolactocin is prepared in 5 steps which includes an indium-mediated
allylation reaction as the key step.
6) Synthetic studies towards the total synthesis of tedanolide: formation of the C
(13)-C(23) fragment.
Abstract:
O SiMe
Me
Me
Me
2 Bu-t
OMe
Me
O
O
OH
OH
I
The C(13)-C(23) subunit (I) of tedanolide was constructed via a boron-mediated s aldol
reaction as key step to control C16 and C17 stereocenters.
7) A highly regioselective indium-mediated allylation of pyridine derivatives:
synthesis of ( )-dihydropinidine from pyridine.
Abtract:
Demonstration of preparation of 1-acyl-1,2-dihydropyridines with high regioselectivity
by indium-mediated allylation of the corresponding 1-acylpyridinium salts is shown. One
application is the synthesis of ()-dihydropinidine such as I.
Me
N
H
Pr-n
I
8) Water-Accelerated Aldol Reaction of Ketene Silyl Acetals with Carbonyl
Compounds
Abstract:
Aldol reactions of ketene silyl acetals with reactive aldehydes function efficiently in
water, producing matching aldol products in good yields. 2-Pyridinecarboxaldehyde (1
mmol) was added to a suspension of ketene silyl acetal Me2C:C(OMe)(OTMS) (2 mmol)
in water (5 mL) to produceMe 3-hydroxy-2,3-dimethyl-3-(2-pyridyl)propanoate in 95%
yield.
9) A remote substituent as control element in indium-mediated allylation reactions
in aqueous media: highly diastereoselective synthesis of 1,3-amino alcohols.
Abstract:
A new way for 1,3-amino alcohols to undergo stereoselective synthesis based on the Inmediated allylation of keto ester (R,S)-I in aqueous media, resulting from shielding of
one face by a remote substituent, developed to be a useful method for acyclic
stereocontrol in the absence of any steric interaction.
Me
COCF
3
N
O
MeO 2 C
CO 2 Me
I
10) Catalytic enantioselective allylation reaction of aldehydes in aqueous medium
Abstract:
A catalyst (S)-Tol-BINAPAgNO3 is successfully applied to a catalytic enantioselective
allylation reaction of aldehydes in aqueous media. The reactions with aromatic
aldehydes lead to the desired products in high yields with good stereoselectivities.
Examples: (S)-Tol-BINAPAgNO3 (0.1 mmol) treated with 1-naphthaldehyde (1 mmol)
and allyltributyltin (1 mmol) in the dark with stirring, resulting in corresponding allyl
alcohol in quant. yield and 81% enantiometric excess (ee).
11) Antioxidants of palm oil: part of their chemistry and insights from feeding
experiments on rabbits.
Abstract:
Tocopherols, tocotrienols and carotenoids, major antioxidants in palm oil, slow down
atheroma development in rabbits feeding on atherogenic diets, and are useed in the body
by different mechanisms exhibited by non-vitamin antioxidants, which also inhibited
atheroma development. Properties of palm oil antioxidants are discussed.
12) Diverse cyclization catalyzed by In(OTf)3 for the convergent assembly of
substituted tetrahydrofurans and tetrahydropyrans.
Abstract:
An l In(OTf) 3-catalyzed (3,5) oxonium-ene type cyclization for the simplistic synthesis
of many multi-substituted tetrahydrofurans and tetrahydropyrans is successfully
developed. Under thermal conditions, the tetrahydrofuran undergoes an In(OTf)3catalyzed skeletal reorganization to its thermodynamic isomer.
13) Synthetic studies toward anisatin: a formal synthesis of (+/-)-8-deoxyanisatin.
Abstract:
There was development of an effective way to construct the C-7a quaternary chiral center
of anisatin via an Eschenmoser- Claisen rearrangement. Also, a formal synthesis of (+/-)8-deoxyanisatin is completed due to conversion of resultant amide to Kende’s epsilonlactose intermediate 3 in four steps.
14) Adaptation to persistent growth in the H9 cell line renders primary isolate of
human immunodeficiency virus type 1 sensitive to neutralization by vaccine sera
Abstract:
7 varied primary isolates of human immunodeficiency virus type 1 (HIV-1) were
discovered to be refractory to neutralization by antisera to recombinant gp120 (rgp120)
protein from HIV-1 MN. This is very different from the sensitivity displayed by some
laboratory-adapted viruses. The difference between primary and laboratory-adapted
viruses lies in their infection. Growth in cell lines is not enough to render primary virus
sensitive to neutralization. The similar changes in neutralization sensitivity with changes
in cell tropism and cytopathic effect propose a common underlying mechanism(s) acting
through the whole envelope protein complex.
14) Evidence for a stem cell-specific repressor of Moloney murine leukemia virus
expression in embryonal carcinoma cells.
Abstract:
A negative regulatory element (NRE) spanning the tRNA primer-binding site (PBS) of
Moloney murine leukemia virus (M-MuLV) shows repression of M-MuLV expression in
embryonal carcinoma (EC) cells. A DNA-binding activity specific for the M-MuLV NRE
was detected in vitro by using crude EC nuclear extracts in exonuclease III protection
assays. Binding is strongly related to repression in EC cells. Mutations within the NRE
that relieve repression disrupt binding activity. Nuclear extracts prepared from EC cell
cultures shows lesser binding activity for the NRE. This shows the presence of a stem
cell-specific repressor that extinguishes M-MuLV expression via the NRE at the tRNA
PBS.
15) Negative regulation of retrovirus expression in embryonal carcinoma cells
mediated by an intragenic domain
Abstract:
An intragenic region spanning the tRNA primer binding site of a MOloney murine
keukemia virus recombinant retrovirus is discovered to restrict expression in embryonal
carcinoma (EC) cells. When inhibitory domain is present, levels of steady-state RNA
created from integrated recombinant templates in stable co-transformation assays were
reduced by 20 times in EC cells. Repression of a template with the EC-specific inhibitory
component is reduced by an excess of specific competitor DNA. Repression by inhibitory
component is orientation independent. The presence of a saturable, trans-acting negative
regulatory factor in EC cells suggest that interaction with the factor with intragenic
inhibitory component occurs at DNA level.
16) Proviral sequences that restrict retroviral expression in mouse embryonal
carcinoma cells.
Abstract:
Embryonal carcinoma (EC) cells do not allow for retrovirus replication. The M-MuLV
long terminal repeat and the long terminal repeat deletions are linked to neo structural
gene sequences that encode resistance to the neomycin analog G418, to investigate the
activity of the Moloney murine leukemia virus (M-MuLV) enhancer and promoter
sequences. Expression data and drug resistance frequencies agree that M-MuLV enhancer
is not active in EC cells but the promoter sequences are functional. A proviral DNA
fragment that encodes the leader RNA sequence of a M-MuLV recombinant retrovirus
restricts expression specifically in EC cells. Deletion analysis of the leader fragment
localizes the inhibitory sequences to a region that spans the M-MuLV tRNA primer
binding site. It is unknown if restriction occurs at a transcriptional or posttranscriptional
level, but steady-state RNA levels in transient expression assays are significantly lower.
Collated by: Serene Loo, CG 01/ 08
Date: 15 January 2008