Applications of camphor-derived chiral auxiliaries in the asymmetric synthesis of α-amino acids and other systems
- Authors: Matjila, Joseph Moemise
- Date: 1998-04
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191501 , vital:45106
- Description: A viable synthetic route to camphor-derived imino lactones as precursors for the asymmetric synthesis of a-amino acids has been established. Several synthetic strategies have been investigated and the required regioisomeric imino lactones were finally obtained via the step-wise condensation of JV-(carbobenzyloxy)glycine with the a-ketols, 3-exo-hydroxycamphor and 2-exo- hydroxy-3-bomanone. Enolates of the camphor imino lactones, generated using potassium tert- butoxide, were reacted with a range of alkyl halides. Dialkylation was observed using the 2-imino lactone, while the regioisomeric 3-imino lactone derivative gave monoalkylated products with diastereoselectivities, shown by NMR spectroscopy, to range from 43% d.e. for the methylated product to > 99% d.e. for larger alkyl groups. The expected preference for endo-alkylation is supported by NMR (chemical shift, coupling constant and NOE) data and was confirmed by acidic hydrolysis of the pentylated 3-imino lactone to afford the known acid. Computer modelling, with the software package HYPERCHEM®, was used to explore the conformational properties of the alkylated products and their enolate precursors. Exploratory work on the enantiomeric beneficiation of racemic amino acids, using alkylated imino lactone derivatives, revealed preferential exo-protonation of the enolate intermediates. Asymmetric Baylis-Hillman reactions between a novel camphor-derived acrylic ester and a range of aldehydes afforded the corresponding 2-(hydroxyalkyl)acrylates in up to 59% d.e., the observed stereoselectivities being sensitive to both steric and electronic factors. Attempts to prepare imino lactone derivatives from ketopinic acid, although unsuccessful, led to the isolation of two novel W-(carbobenzyloxy)glycinates, whose structures were established by 1- and 2-D NMR spectroscopy. Attempts to prepare "BINAP" analogues from dibomyl ether's also proved unsuccessful, but the investigation led to the discovery of a third, novel dibomyl ether. , Thesis (PhD) -- Faculty of Science, Chemistry, 1998
- Full Text:
- Date Issued: 1998-04
- Authors: Matjila, Joseph Moemise
- Date: 1998-04
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191501 , vital:45106
- Description: A viable synthetic route to camphor-derived imino lactones as precursors for the asymmetric synthesis of a-amino acids has been established. Several synthetic strategies have been investigated and the required regioisomeric imino lactones were finally obtained via the step-wise condensation of JV-(carbobenzyloxy)glycine with the a-ketols, 3-exo-hydroxycamphor and 2-exo- hydroxy-3-bomanone. Enolates of the camphor imino lactones, generated using potassium tert- butoxide, were reacted with a range of alkyl halides. Dialkylation was observed using the 2-imino lactone, while the regioisomeric 3-imino lactone derivative gave monoalkylated products with diastereoselectivities, shown by NMR spectroscopy, to range from 43% d.e. for the methylated product to > 99% d.e. for larger alkyl groups. The expected preference for endo-alkylation is supported by NMR (chemical shift, coupling constant and NOE) data and was confirmed by acidic hydrolysis of the pentylated 3-imino lactone to afford the known acid. Computer modelling, with the software package HYPERCHEM®, was used to explore the conformational properties of the alkylated products and their enolate precursors. Exploratory work on the enantiomeric beneficiation of racemic amino acids, using alkylated imino lactone derivatives, revealed preferential exo-protonation of the enolate intermediates. Asymmetric Baylis-Hillman reactions between a novel camphor-derived acrylic ester and a range of aldehydes afforded the corresponding 2-(hydroxyalkyl)acrylates in up to 59% d.e., the observed stereoselectivities being sensitive to both steric and electronic factors. Attempts to prepare imino lactone derivatives from ketopinic acid, although unsuccessful, led to the isolation of two novel W-(carbobenzyloxy)glycinates, whose structures were established by 1- and 2-D NMR spectroscopy. Attempts to prepare "BINAP" analogues from dibomyl ether's also proved unsuccessful, but the investigation led to the discovery of a third, novel dibomyl ether. , Thesis (PhD) -- Faculty of Science, Chemistry, 1998
- Full Text:
- Date Issued: 1998-04
Southern African Journal of Gerontology, volume 7, number 1, April 1998
- Ferreira, Monica (editor), Moller, Valerie, HSRC/UCT Centre for Gerontology
- Authors: Ferreira, Monica (editor) , Moller, Valerie , HSRC/UCT Centre for Gerontology
- Date: 1998
- Subjects: Gerontology -- South Africa , Older people -- Care -- South Africa
- Language: English
- Type: Text
- Identifier: vital:8076 , http://hdl.handle.net/10962/d1012871
- Description: [From Editorial] Each of the papers in this number of SAJG deals with dilemmas and issues in the matter of public and private care for older persons in southern Africa. Three papers deal explicitly with South Africa's social-security system·- specifically the old-age pension. Two papers deal with residential care models. And a sixth paper examines informal caregiving. In an expansive overview of public finance and ageing in South Africa, Van der Berg examines budgetary expenditure on the older population and places the magnitude and function of the social-pension system in perspective. The author briefly traces the historical evolution of the system. In a paper based on extensive archival research, Sagner details the history of the pension from 1920 to 1960 and shows that numerous contemporary pension-related issues are no different to issues of past decades. In her paper, Oakley examines the effects of recent changes in social-welfare policy on the residents and administrators of a home for marginalized older people in a remote South African town. She contends that new policy erroneously assumes that marginalized and historically disadvantaged older individuals are able to live self-sufficiently within the bosom of family - in a spirit of ubuntu. Ackermann and Matebesi report on a study of the experiences of carers of older family members in an African township and consider how these carers, who have few resources, could be assisted and supported in their care giving tasks. Mupedziswa describes the nature and functioning of an alternative residential care model in Zimbabwe - a cooperative living scheme specifically established to enable destitute and socially-impoverished older people to co-reside in a safe and mutually-supportive environment. Moller gives readers an insightful update and analysis of the January 1998 pension payment debacle in the Eastern Cape Province, when the payment of more than 600 000 pensioners was delayed because of provincial-government management errors. Finally, SAJG welcomes Wilson's announcement in a letter to the editor of the establishment of AFRIT A, whose aims are to promote and to co-ordinate linkages between training and research initiatives on ageing and policy structures in African countries.
- Full Text:
- Date Issued: 1998
- Authors: Ferreira, Monica (editor) , Moller, Valerie , HSRC/UCT Centre for Gerontology
- Date: 1998
- Subjects: Gerontology -- South Africa , Older people -- Care -- South Africa
- Language: English
- Type: Text
- Identifier: vital:8076 , http://hdl.handle.net/10962/d1012871
- Description: [From Editorial] Each of the papers in this number of SAJG deals with dilemmas and issues in the matter of public and private care for older persons in southern Africa. Three papers deal explicitly with South Africa's social-security system·- specifically the old-age pension. Two papers deal with residential care models. And a sixth paper examines informal caregiving. In an expansive overview of public finance and ageing in South Africa, Van der Berg examines budgetary expenditure on the older population and places the magnitude and function of the social-pension system in perspective. The author briefly traces the historical evolution of the system. In a paper based on extensive archival research, Sagner details the history of the pension from 1920 to 1960 and shows that numerous contemporary pension-related issues are no different to issues of past decades. In her paper, Oakley examines the effects of recent changes in social-welfare policy on the residents and administrators of a home for marginalized older people in a remote South African town. She contends that new policy erroneously assumes that marginalized and historically disadvantaged older individuals are able to live self-sufficiently within the bosom of family - in a spirit of ubuntu. Ackermann and Matebesi report on a study of the experiences of carers of older family members in an African township and consider how these carers, who have few resources, could be assisted and supported in their care giving tasks. Mupedziswa describes the nature and functioning of an alternative residential care model in Zimbabwe - a cooperative living scheme specifically established to enable destitute and socially-impoverished older people to co-reside in a safe and mutually-supportive environment. Moller gives readers an insightful update and analysis of the January 1998 pension payment debacle in the Eastern Cape Province, when the payment of more than 600 000 pensioners was delayed because of provincial-government management errors. Finally, SAJG welcomes Wilson's announcement in a letter to the editor of the establishment of AFRIT A, whose aims are to promote and to co-ordinate linkages between training and research initiatives on ageing and policy structures in African countries.
- Full Text:
- Date Issued: 1998
- «
- ‹
- 1
- ›
- »