Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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A research roadmap for quantifying non-state and subnational climate mitigation action
Hsu, Angel ; Höhne, Niklas ; Kuramochi, Takeshi ; Roelfsema, Mark ; Weinfurter, Amy ; Xie, Yihao ; Lütkehermöller, Katharina ; Chan, Sander ; Corfee-Morlot, Jan ; Drost, Philip ; Faria, Pedro ; Gardiner, Ann ; Gordon, David J. ; Hale, Thomas ; Hultman, Nathan E. ; Moorhead, John ; Reuvers, Shirin ; Setzer, Joana ; Singh, Neelam ; Weber, Christopher ; Widerberg, Oscar - \ 2019
Nature Climate Change 9 (2019)1. - ISSN 1758-678X - p. 11 - 17.

Non-state and subnational climate actors have become central to global climate change governance. Quantitatively assessing climate mitigation undertaken by these entities is critical to understand the credibility of this trend. In this Perspective, we make recommendations regarding five main areas of research and methodological development related to evaluating non-state and subnational climate actions: defining clear boundaries and terminology; use of common methodologies to aggregate and assess non-state and subnational contributions; systematically dealing with issues of overlap; estimating the likelihood of implementation; and addressing data gaps.

Are the G20 economies making enough progress to meet their NDC targets?
Elzen, Michel den; Kuramochi, Takeshi ; Höhne, Niklas ; Cantzler, Jasmin ; Esmeijer, Kendall ; Fekete, Hanna ; Fransen, Taryn ; Keramidas, Kimon ; Roelfsema, Mark ; Sha, Fu ; Soest, Heleen van; Vandyck, Toon - \ 2019
Energy Policy 126 (2019). - ISSN 0301-4215 - p. 238 - 250.
China - G20 economies - National climate and energy policies - NDCs - Paris Agreement

Under the Paris Agreement, countries committed to a variety of climate actions, including post-2020 greenhouse gas (GHG) emissions reduction targets. This study compares projected GHG emissions in the G20 economies under current climate policies to those under the GHG targets outlined in the nationally determined contributions (NDCs). It is based on an assessment of official governmental estimates and independent national and global studies. The study concludes that six G20 members (China, India, Indonesia, Japan, Russia and Turkey) are projected to meet their unconditional NDC targets with current policies. Eight members (Argentina, Australia, Canada, the European Union, Republic of Korea, South Africa and the United States) require further action to achieve their targets. Insufficient information is available for Saudi Arabia, and emission projections for Brazil and Mexico are subject to considerable uncertainty. The study also presents high-level decarbonisation indicators to better understand the current progress towards meeting the NDCs – Saudi Arabia and South Africa were found to continue increasing both emission intensity per unit GDP and emissions per capita under current policies by 2030 from 2015 levels.

Reducing global GHG emissions by replicating successful sector examples : the ‘good practice policies’ scenario
Roelfsema, Mark ; Fekete, Hanna ; Höhne, Niklas ; Elzen, Michel den; Forsell, Nicklas ; Kuramochi, Takeshi ; Coninck, Heleen de; Vuuren, Detlef P. van - \ 2018
Climate Policy 18 (2018)9. - ISSN 1469-3062 - p. 1103 - 1113.
2°C limit - Enhancing ambition - integrated assessment modelling - sector indicators - successful policies
This article shows the potential impact on global GHG emissions in 2030, if all countries were to implement sectoral climate policies similar to successful examples already implemented elsewhere. This assessment was represented in the IMAGE and GLOBIOM/G4M models by replicating the impact of successful national policies at the sector level in all world regions. The first step was to select successful policies in nine policy areas. In the second step, the impact on the energy and land-use systems or GHG emissions was identified and translated into model parameters, assuming that it would be possible to translate the impacts of the policies to other countries. As a result, projected annual GHG emission levels would be about 50 GtCO2e by 2030 (2% above 2010 levels), compared to the 60 GtCO2e in the ‘current policies’ scenario. Most reductions are achieved in the electricity sector through expanding renewable energy, followed by the reduction of fluorinated gases, reducing venting and flaring in oil and gas production, and improving industry efficiency. Materializing the calculated mitigation potential might not be as straightforward given different country priorities, policy preferences and circumstances. Key policy insightsConsiderable emissions reductions globally would be possible, if a selection of successful policies were replicated and implemented in all countries worldwide.This would significantly reduce, but not close, the emissions gap with a 2°C pathway.From the selection of successful policies evaluated in this study, those implemented in the sector ‘electricity supply’ have the highest impact on global emissions compared to the ‘current policies’ scenario.Replicating the impact of these policies worldwide could lead to emission and energy trends in the renewable electricity, passenger transport, industry (including fluorinated gases) and buildings sector, that are close to those in a 2°C scenario.Using successful policies and translating these to policy impact per sector is a more reality-based alternative to most mitigation pathways, which need to make theoretical assumptions on policy cost-effectiveness.
Effect of exercise on apparent total tract digestibility of nutrients and faecal recovery of ADL and TiO2 in ponies
Schaafstra, F.J.W.C. ; Doorn, D.A. van; Schonewille, J.T. ; Roelfsema, E. ; Westermann, C.M. ; Dansen, O. ; Jacobs, M. ; Lee, J.Y. ; Spronck, E.A. ; Blok, M.C. ; Hendriks, W.H. - \ 2018
Animal 12 (2018)12. - ISSN 1751-7311 - p. 2505 - 2510.
digestibility - equines - exercise - markers - total faeces collection
Exercise and physical training are known to affect gastrointestinal function and digestibility in horses and can lead to inaccurate estimates of nutrient and energy digestibility when markers are used. The effect of exercise on apparent nutrient digestibility and faecal recoveries of ADL and TiO2 was studied in six Welsh pony geldings subjected to either a low- (LI) or high-intensity (HI) exercise regime according to a cross-over design. Ponies performing LI exercise were walked once per day for 45 min in a horse walker (5 km/h) for 47 consecutive days. Ponies submitted to HI exercise were gradually trained for the same 47 days according a standardized protocol. Throughout the experiment, the ponies received a fixed level of feed and the daily rations consisted of 4.7 kg DM of grass hay and 0.95 kg DM of concentrate. The diet was supplemented with minerals, vitamins and TiO2 (3.0 g Ti/day). Total tract digestibility of DM, organic matter (OM), CP, crude fat, NDF, ADF, starch, sugar and energy was determined with the total faeces collection (TFC) method. In addition, DM and OM digestibility was estimated using internal ADL and the externally supplemented Ti as markers. Urine was collected on the final 2 days of each experimental period. Exercise did not affect apparent digestibility of CP, crude fat, starch and sugar. Digestibility of DM (DMD), OM (OMD), ADF and NDF tended to be lower and DE was decreased when ponies received the HI exercise regime. For all treatments combined, mean faecal recoveries of ADL and Ti were 87.8±1.7% and 99.3±1.7%, respectively. Ti was not detected in the urine, indicating that intestinal integrity was maintained with exercise. Dry matter digestibility estimated with the TFC, ADL and Ti for ponies subjected to LI exercise were 66.3%, 60.3% and 64.8%, respectively, while DMD for HI ponies were 64.2%, 60.3% and 65.2%, respectively. In conclusion, physical exercise has an influence on the GE digestibility of the feed in ponies provided with equivalent levels of feed intake. In addition, the two markers used for estimating apparent DMD and OMD indicate that externally supplemented Ti is a suitable marker to determine digestibility of nutrients in horses performing exercise unlike dietary ADL.
The traditional Chinese philosophies in inter-cultural leadership : The case of Chinese expatriate managers in the Dutch context
Lin, Li ; Li, Peter Ping ; Roelfsema, Hein - \ 2018
Cross Cultural and Strategic Management 25 (2018)2. - ISSN 2059-5794 - p. 299 - 336.
China - Confucianism - Daoism - Dutch - Expatriate leadership - Legalism
Purpose: As the global presence of Chinese firms grows, increasing numbers of Chinese managers are working abroad as expatriates. However, little attention has been paid to such Chinese expatriate managers and their leadership challenges in an inter-cultural context, especially across a large cultural distance. To fill the gap in the literature concerning the leadership challenges for expatriate managers in an inter-cultural context, the purpose of this paper is to elucidate the leadership styles of Chinese expatriate managers from the perspectives of three traditional Chinese philosophies (i.e. Confucianism, Taoism, and Legalism) in the inter-cultural context of the Netherlands. Design/methodology/approach: The data for this qualitative study were collected via semi-structured, open-ended, narrative interviews with 30 Chinese expatriate managers in the Netherlands. Findings: The results clearly show that the leadership style of Chinese expatriate managers is deeply rooted in the three traditional Chinese philosophies of Confucianism, Taoism, and Legalism, even in an inter-cultural context. Specifically, the study reveals two salient aspects of how Chinese expatriate managers frame and interact with a foreign cultural context from the perspectives of traditional Chinese philosophies. First, the Chinese expatriate managers reported an initial cultural shock related to frictions between the foreign cultural context and Confucianism or Taoism, but less so in the case of Legalism. Second, the Chinese expatriate managers also reported that their interactions with the Dutch culture are best described as a balance between partial conflict and partial complementarity (thus, a duality). In this sense, the leadership style of Chinese expatriate managers is influenced jointly by the three traditional Chinese philosophies and certain elements of the foreign cultural context. This is consistent with the Chinese perspective of yin-yang balancing. Originality/value: This study is among the first to offer a more nuanced and highly contextualized understanding of leadership in the unique case of expatriate managers from an emerging market (e.g. China) in an advanced economy (e.g. the Netherlands). The authors call for more research to apply the unique perspective of yin-yang balancing in an inter-cultural context. The authors posit that this approach represents the most salient implication of this study. For practical implications, the authors argue that expatriate leaders should carefully manage the interplay between their deep-rooted home-country philosophies and their salient host-country culture. Reflecting on traditional philosophies in another culture can facilitate inter-cultural leadership training for Chinese expatriates.
Greenhouse gas emissions from current and enhanced policies of China until 2030 : Can emissions peak before 2030?
Elzen, Michel den; Fekete, Hanna ; Höhne, Niklas ; Admiraal, Annemiek ; Forsell, Nicklas ; Hof, A.F. ; Olivier, J.G.J. ; Roelfsema, Mark ; Soest, Heleen van - \ 2016
Energy Policy 89 (2016). - ISSN 0301-4215 - p. 224 - 236.
Climate agreement - National climate and energy policies - Renewable targets

In June 2015, China announced its post-2020 reduction targets, its central element being the intention to peak CO2 emissions by 2030 or earlier. China has implemented several policies to reduce its greenhouse gas (GHG) emissions. This study provides emission projections for China up to 2030 given current policies and a selected set of enhanced policies, and compares the results with projected CO2 emission trajectories that are consistent with the announced target for 2030. The projections are based on existing scenarios and energy system and land use model calculations. We project that the 2030 CO2 emission level consistent with a peak in CO2 emissions by 2030 ranges from 11.3 to 11.8 GtCO2. The corresponding total GHG emission level ranges from 13.5 to 14.0 GtCO2e in 2030. Current policies are likely not to be sufficient to achieve the 2030 targets, as our projected total GHG emission level under current policies ranges from 14.7 to 15.4 GtCO2e by 2030. However, an illustrative set of enhancement policy measures, all of which are related to national priorities, leads to projected GHG emission levels from 13.1 to 13.7 GtCO2e by 2030 - and thus below the levels necessary for peaking CO2 emissions before 2030.

Risk factors associated with health disorders in sport and leisure horses in The Netherlands
Visser, E.K. ; Neijenhuis, F. ; Graaf-Roelfsema, E. de; Wesselink, H.G.M. ; Boer, J. de; Wijhe-Kiezebrink, M.C. van; Engel, B. ; Reenen, C.G. van - \ 2014
Journal of Animal Science 92 (2014)2. - ISSN 0021-8812 - p. 844 - 855.
respiratory-disease - insulin-resistance - part 1 - prevalence - management - obesity - welfare - laminitis - inference - responses
Horses are used for a wide variety of purposes from being used for recreational purposes to competing at an international level. With these different uses, horses have to adapt to numerous challenges and changes in their environment, which can be a challenge itself in continuously safeguarding their welfare. The objective of this study was to assess the prevalence of health disorders with clinical examination and identify possible risk factors of health disorders affecting horse welfare in professional husbandry systems in the Netherlands. With the use of fixed protocols for recording health aspects in horses, 150 horse farms voluntarily participating in the study were assessed by trained assessors. On each farm, 20 horses were clinically examined, in total almost 3,000 animals. This study recorded on the basis of the clinical examinations: the respiratory system (i.e., abnormal breathing [1%], coughing [1%], nasal discharge [1.9%]), body condition (i.e., 18.8% fat body condition and 6.4% poor body condition), locomotion (14.5% exhibited irregularity of locomotion and 4.8% were lame), back palpation (a light response [22.6%] and moderate to severe response [8.4%]), mouth (i.e., irregularities on mouth corners [3.4%] and bars [3.4%]), and ocular discharge (12%). Risk factor analysis, stepwise using mixed model regression, demonstrated several risk factors for health aspects. Horses used for instruction (riding lessons) were almost two times more at risk to develop moderate to severe back pain compared to horses used for recreation (odds ratios [OR] = 0.54) or for competition (OR = 0.61). Horses used for instruction (riding school lessons), breeding, or recreation all had a higher risk for irregular locomotion or lameness compared to competition horses (OR = 0.42, OR = 0.55, OR = 2.14, respectively). Horses used for recreation were more prone to have a higher BCS compared to horses used for breeding (OR = 3.07) and instruction (OR = 2.06). The prevalence of health problems and the identified risk factors are valid for the horses in the present study in which farms voluntarily participated. Furthermore, the results may provide the basis for horse welfare and health programs on farm and horse industry levels. With the development of a valid welfare monitoring system for the horse industry, the welfare of horses can be increased through improving awareness and stimulating changes in management.
Are major economies on track to achieve their pledges for 2020? An assessment of domestic climate and energy policies
Roelfsema, M. ; Elzen, M.G.J. den; Hoehne, N.E. ; Hof, A.F. ; Braun, N. ; Fekete, H. ; Böttcher, H. ; Brandsma, R. ; Larkin, J. - \ 2014
Energy Policy 67 (2014). - ISSN 0301-4215 - p. 781 - 796.
gas emission reductions - annex i countries
Many of the major greenhouse gas emitting countries have planned and/or implemented domestic mitigation policies, such as carbon taxes, feed-in tariffs, or standards. This study analyses whether the most effective national climate and energy policies are sufficient to stay on track for meeting the emission reduction proposals (pledges) that countries made for 2020. The analysis shows that domestic policies of India, China and Russia are projected to lead to lower emission levels than the pledged levels. Australia's and the EU's nationally legally binding policy framework is likely to deliver their unconditional pledges, but not the conditional ones. The situation is rather unclear for Japan, South Korea, Brazil and Indonesia. We project that policies of Canada and the USA will reduce 2020 emission levels, but additional policies are probably needed to deliver their pledges in full. The analysis also shows that countries are implementing policies or targets in various areas to a varying degree: all major countries have set renewable energy targets; many have recently implemented efficiency standards for cars, and new emission trading systems are emerging.
Testen op overtraining
Pas, M.F.W. te; Wijnberg, I. ; Graaf-Roelfsema, Ellen ; Kolk, Han van der - \ 2013
Paard & Sport (2013)7. - ISSN 1388-0047 - p. 2 - 4.
Als een mens of een paard traint, treden lichamelijke
veranderingen op. Het lichaam past
zich aan de gevraagde inspanning aan. Dit is
een normaal proces. Soms is sprake van
overtraining,
met ongewenste effecten. Hoe
voorkom je dit? Wetenschappers en veterinairen
werken samen aan een preventieve test.
Brachyspira Species and Gastroenteritis in Humans
Westerman, L.J. ; Boer, R.F. de; Roelfsema, J.H. ; Friesema, I.H.M. ; Kortbeek, L.M. ; Wagenaar, J.A. ; Bonten, M.J.M. ; Kusters, J.G. - \ 2013
Journal of Clinical Microbiology 51 (2013)7. - ISSN 0095-1137 - p. 2411 - 2413.
human intestinal spirochetosis - homosexual-men - clinical-significance - risk-factors - aalborgi - pilosicoli - diarrhea - netherlands - infection - mucosa
Brachyspira species have been implicated as a potential cause of gastroenteritis in humans; this is, however, controversial. In 733 gastroenteritis cases and 464 controls, we found 29 samples positive for Brachyspira species (2.3% of cases and 2.6% of controls; P = 0.77). Brachyspira species were not associated with gastroenteritis in humans.
Skeletal muscle transcriptome profiles related to different training intensities and detraining in Standardbred horses: A search for overtraining biomarkers
Pas, M.F.W. te; Wijnberg, I.D. ; Hoekman, A.J.W. ; Graaf-Roelfsema, E. de; Keizer, H. ; Breda, E. van; Ducro, B.J. ; Kolk, J.H. van der - \ 2013
The Veterinary Journal 197 (2013)3. - ISSN 1090-0233 - p. 717 - 723.
nonspecific immunity - extracellular-matrix - maximal exercise - heart-rate - resistance - adaptation - responses - insulin - blood - variability
Training horses improves athletic capabilities by inducing skeletal muscle-specific and systemic adaptations. However, rest is required to recover from exercise or else overtraining may occur and affect performance and welfare. Biomarkers would be useful to identify early chronic overtraining in animals. The objective of the current study was to investigate skeletal muscle gene expression patterns and underlying biological mechanisms related to training of different intensities and detraining. Untrained 20 month-old Standardbred geldings were exercised at varying intensities (endurance and sprint) followed by detraining (n = 5 per phase). The results indicated that training mainly affected skeletal muscle-specific protein metabolism and increased CO2 export from the tissues. Intensive training increased energy metabolism and affected heart and adipose tissues, while having an adverse effect on stress, apoptosis and immune capacity. The intensity of the training could be related to decreased expression of extra cellular matrix proteins (ECM), cell–cell contacts and intracellular signalling pathways. During detraining, most mechanisms were reversed, but heart tissue-related changes and increased expression of skeletal muscle-specific proteins were still evident. The study suggested that changes to ECM expression and cell–cell contact mechanisms may be long-lasting and related to multifactorial aspects of training and detraining. These biomarkers may be useful to identify horses in the early stages of chronic overloading or early overtraining.
Greenhouse gas emission reduction proposals and national climate policies of major economies : Policy Brief
Hoehne, N.E. ; Braun, N. ; Fekete, H. ; Larkin, J. ; Elzen, M. ; Roelfsema, M. ; Hof, A. van 't; Böttcher, H. - \ 2012
Bilthoven, Utrecht : Netherlands Environmental Assessment Agency, Bilthoven and ECOFYS, Utrecht (ECOFYS : sustainable energy for everyone ) - 33
Zoonotic parasites in fecal samples and fur from dogs and cats in The Netherlands
Overgaauw, P.A.M. ; Zutphen, L. van; Hoek, D. ; Yaya, F.O. ; Roelfsema, J. ; Pinelli, E. ; Knapen, F. van; Kortbeek, L.M. - \ 2009
Veterinary Parasitology 163 (2009)1-2. - ISSN 0304-4017 - p. 115 - 122.
ocular larva migrans - toxocara-canis - animal shelters - cryptosporidium - giardia - epidemiology - infections - children - transmission - eggs
Pets may carry zoonotic pathogens for which owners are at risk. The aim of the study is to investigate whether healthy pets harbour zoonotic parasitic infections and to make an inventory of the interactions between pet-owners and their companion animals in the Netherlands. Fecal and hair samples were collected from healthy household dogs and cats in Dutch veterinary practices. Owners were interviewed about interaction with their pets. The samples were investigated by microscopy, ELISA, and PCR. From 159 households, 152 dogs (D) and 60 cats (C), information and samples were collected and examination for several zoonotic parasites was performed. Toxocara eggs were found in 4.4% (D) and 4.6% (C) of the fecal samples and in 12.2% (D) and 3.4% (C) of the fur samples. The median epg in the fur was 17 (D) and 28 (C) and none of these eggs were viable. From 15.2% of the dog and 13.6% of the cat feces Giardia was isolated. One canine and one feline Giardia isolate was a zoonotic assemblage A (12%). Cryptosporidium sp. were present in 8.7% (D) and 4.6% (C) of the feces. Fifty percent of the owners allow the pet to lick their faces. Sixty percent of the pets visit the bedroom; 45¿60% (D¿C) are allowed on the bed, and 18¿30% (D¿C) sleep with the owner in bed. Six percent of the pets always sleep in the bedroom. Of the cats, 45% are allowed to jump onto the kitchen sink. Nearly 39% of the dog owners never clean up the feces of their dog. Fifteen percent of the dog owners and 8% of the cat owners always wash their hands after contact with the animals. Close physical contact between owners and their pets is common and poses an increased risk of transmission of zoonotic pathogens. Education of owners by the vet, specifically about hygiene and potential risks, is required
The precalence of the metabolic syndrome is increades in patients with GH deficiency, irrespective of long-term substition with recombinant human GH
Klaauw, A.A. ; Biermasz, N.R. ; Feskens, E.J.M. ; Bos, M.B. ; Smit, J.W. ; Roelfsema, F. ; Corssmit, E.P. ; Pijl, H. ; Romijn, J.A. ; Pereira, A.M. - \ 2007
European Journal of Endocrinology 156 (2007)4. - ISSN 0804-4643 - p. 455 - 462.
growth-hormone gh - cardiovascular risk-factors - replacement therapy - hypopituitary patients - insulin sensitivity - cushings-disease - adults - cholesterol - resistance - mortality
Objectives: Many reports demonstrate improvements in cardiovascular risk factors during GH replacement (rhGH) in adult GH deficiency (GHD). However, it remains to be determined to what extent these changes translate into a reduction of increased cardiovascular morbidity and mortality. The aim of this study was to evaluate the effects of long-term rhGH replacement on the prevalence of the metabolic syndrome (MS). Design, settings, main outcome measures: The MS was scored by the National Cholesterol Education Program-Adult Treatment Panel III definition in 50 consecutive GHD patients (45 9 years of age), before and after 2 and 5 years of rhGH replacement, and the data of untreated patients were compared with the general population using data from a Dutch population-based study (n = 1062, 44 +/- 8 years of age). Results: Hypertriglyceridaemia (46.0 vs 18.5%, P <0.0001), hypertension (66.0 vs 35.5%, P <0.0001) and abdominal obesity (38.0 vs 23.4%, P=0.0178) were more prevalent in untreated patients when compared with controls, resulting in a higher prevalence of the MS in patients (38.0 vs 15.7%, P <0.0001). During rhGH replacement at a mean dose of 0.5 +/- 0.2 mg/day resulting in IGF-I concentrations in the normal age-adjusted reference range, mean high-density lipoprotein cholesterol level increased compared with baseline (P <0.001). However, the prevalence of (components of) the MS did not change after 2 or 5 years of treatment with rhGH. Conclusion: In this study, the prevalence of the MS in patients with GHD is increased compared with healthy controls, irrespective of rhGH replacement.
Using dilution techniques and multifrequency bioelectrical impedance to assess both total body water and extracellular water at baseline and during recombinant human growth hormone (GH) treatment in GH deficient adults.
Janssen, Y.J.H. ; Deurenberg, P. ; Roelfsema, F. - \ 1997
Journal of Clinical Endocrinology and Metabolism 82 (1997). - ISSN 0021-972X - p. 3349 - 3355.
Serum leptin levels during recombinant human GH therapy in adults with GH deficiency.
Janssen, Y.J.H. ; Frölich, M. ; Deurenberg, P. ; Roelfsema, F. - \ 1997
European Journal of Endocrinology 137 (1997). - ISSN 0804-4643 - p. 650 - 654.
Effect of administration of growth hormone on plasma and intracellular levels of thyroxine and tri-iodothyronine in thyroidectomized thyroxine-treated rats.
Geelhoed-Duijvestijn, P.H.L.M. ; Roelfsema, F. ; Schröder-van der Elst, J.P. ; Doorn, J. van; Heide, D. van der - \ 1992
Journal of Endocrinology 133 (1992). - ISSN 0022-0795 - p. 45 - 49.
Aminering van hydroxyderivaten van halogeenazahetarenen
Roelfsema, W.A. - \ 1972
Landbouwhogeschool Wageningen. Promotor(en): H.J. den Hertog. - Wageningen : Veenman - 57
pyridines - piperidinen - derivaten - chinolinen - chinoline - indolen - chemische reacties - aminen - pyrrool - pyridines - piperidines - derivatives - quinolines - quinoline - indoles - chemical reactions - amines - pyrrole

In this thesis an introductory investigation is described on the reactivity of hydroxy derivatives of halogenopyridines and a bromohydroxyquinoline towards strong bases.

It is a sequel to earlier work on the effect of substituents present in the nucleus of halogenopyridines on the course of aminations of these substances (chapter 1).

Halogenohydroxy compounds were reacted with potassium amide or lithium piperidide, whereupon products were isolated, identified and determined quantitatively. Mechanisms were suggested interpreting the results obtained. Details about amination procedures and analyses of reaction mixtures are given in chapter 2.

When various halogenohydroxypyridines are reacted with potassium amide in liquid ammonia at -33°C, substitutions, cine-substitutions and ring contractions occur.

It was shown that part of the bromohydroxypyridines are aminated according to the elimination-addition (EA)mechanism via hydroxy-3,4-didehydropyridines as intermediates. The addition of ammonia to the triple bond in the intermediate is directed by the hydroxy group. Depending on this effect one or two aminohydroxy compounds are formed. Thus, cine-substitution takes place exclusively in the transformation of 3-bromo-5-hydroxypyridine via 5-hydroxy-3,4-didehydropyridine into 4-amino-5-hydroxypyridine. The amination of 4-bromo-2-hydroxypyridine follows a more complicated pattern, presumably involving two isomeric hydroxydidehydropyridines. It leads to the formation of a mixture of 3- and 4- amino-2-hydroxypyridine (chapter 3).

From both 2- and 3-bromo-4-hydroxypyridine, 2-amino-4-hydroxypyridine is formed. These reactions can be explained, assuming divergent AE-processes (chapter 4).

The amination of 2-bromo-6-hydroxypyridine takes place without rearrangement. Continued investigation is required to establish whether this process follows the AE pathway.

Remarkable results were met when studying the amination of 2-chloro-3-hydroxypyridine, 2-bromo-3-hydroxypyridine and three derivatives of the latter. These substances change into pyrrole derivatives. In contrast to the reaction of 3-amino-2-bromopyridine with potassium amide yielding 3-cyanopyrrole, the halogeno-hydroxypyridines are converted into pyrrole carbonamides, in which the substituent occupies the 2-position. A 3-substituted pyrrole derivative was obtained from our substrates however, when lithium piperidide was used as a reagent. Together with this product (i.e. pyrrole-3-carbopiperidide), 3-hydroxy-2-piperidinopyridine is obtained. The mechanism of the reactions of 2-halogeno-3- hydroxypyridines and those of the corresponding amino and methyl compounds are discussed (chapter 5).

Ring contraction takes place too in the amination with potassium amide, of 4-bromo-3-hydroxyquinoline i.e. a derivative of 4-bromo-3-hydroxypyridine from which no hydrogen bromide can be abstracted leading to the formation of a 4,5-didehydro compound. In this reaction oxindole is the product. Thus, along with the ring-fission a fragment of the chain is split off containing one carbon atom, yielding cyanide.

By the action of lithium piperidide or of piperidine at elevated temperature on 3-bromo-4-hydroxyquinoline the ring system remains unaltered. In the former case 3-hydroxy-4-piperidinoquinoline is formed as a substitution product, in the latter a cine-substitution results in the formation of 3-hydroxy-2-piperidinoquinoline.

Mechanisms were proposed for the reactions of 4-bromo-3-hydroxyquinoline; they were compared again with those, suggested for the aminations of the corresponding amino compound (chapter 6).

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