title: pH Sensitive Anticancer Prodrug: Amide of Kemp's Acid

authors: Brooks, Robert Turongo

subjects: Amide hydrolysis kinetics

abstract: Solid tumours are characterised by lower extracellular pH (as low as 5.8 pH) compared to normal healthy cellular pH (actively regulated at pH 7.3). This difference may be exploited with an acid-sensitive anti-tumour prodrug which releases a cytotoxin selectively in tumour tissue.
The research reported in this thesis was aimed at synthesising and performing rate studies on an amide prodrug with pH-sensitive rates of reaction in the pH 5 - 8 region. Amide hydrolysis is catalysed by neighbouring carboxylic acid groups in their fully protonated state but not in its ionised state (shown in the figure below), whereby pH sensitivity around pH 5 - 8 can be exploited. The current study was carried out on an amide of Kemp's acid which, due to enforced stereochemistry of carboxylic acid and amide functional groups, has the type of structure conducive to accelerated amide hydrolysis.
 
The rates for tertiary and secondary aliphatic amides of this Kemp's acid system have shown high reactivity at low pH and a large reduction in rate across pH 5.8 - 7.3, however an aryl amide had not previously been studied. It was thought that an aryl amide of Kemp's acid would provide a faster rate of reaction compared with the alkyl amides, and also aryl amine cytotoxins exist which could be attached as an amide.
A secondary aryl amide of Kemp's acid (58) was obtained via a potassium hydroxide ring-opening reaction on a synthesised imide of Kemp's acid (43).  
 
Aliquots of the ring-opened amide (58) were added to buffered (phosphate and malonate) aqueous solutions (with ionic strength   = 1 mol L-1) and the hydrolysis reaction followed at 30.0 oC across the pH range 0.48 - 8. First order rate constants were calculated from absorbance change with time and the pH-rate profile established. Absorbance changes were shown to be consistent with amide hydrolysis with no evidence of any imide reformation as evident in other studies. The rate data were analysed. There was no evidence from rates for the two successive acid ionisations with only a single rate plateau evident from pH 2 to 5, suggesting that both di- and mono-acid species have very similar hydrolysis rates or that the second ionisation is low due to stabilisation of the mono-ionised molecule by hydrogen bonding interactions. For this reason, the rate profile could be analysed only as if it were a single ionisation in the same way that Menger and Ladika analysed their aliphatic tertiary pyrrolidyl amide in an earlier study. This analysis gave a pKa value of 6.72   0.09 and a limiting rate constant of 7.1 x 10-5 s-1. The studies revealed a three fold rate differential between pH 5.8 (faster) versus 7.3 (slower), a difference which is probably too small a selectivity for possible prodrug application.
Separately, the second order rate coefficient for the reaction of potassium hydroxide solution to open the imide was also established (k2 = 0.00067 L mol-1 s-1 at 30.0 oC,   = 1.00 mol L-1 with KCl).

text: pH Sensitive Anticancer Prodrug: Amide of Kemp's Acid Solid tumours are characterised by lower extracellular pH (as low as 5.8 pH) compared to normal healthy cellular pH (actively regulated at pH 7.3). This difference may be exploited with an acid-sensitive anti-tumour prodrug which releases a cytotoxin selectively in tumour tissue.
The research reported in this thesis was aimed at synthesising and performing rate studies on an amide prodrug with pH-sensitive rates of reaction in the pH 5 - 8 region. Amide hydrolysis is catalysed by neighbouring carboxylic acid groups in their fully protonated state but not in its ionised state (shown in the figure below), whereby pH sensitivity around pH 5 - 8 can be exploited. The current study was carried out on an amide of Kemp's acid which, due to enforced stereochemistry of carboxylic acid and amide functional groups, has the type of structure conducive to accelerated amide hydrolysis.
 
The rates for tertiary and secondary aliphatic amides of this Kemp's acid system have shown high reactivity at low pH and a large reduction in rate across pH 5.8 - 7.3, however an aryl amide had not previously been studied. It was thought that an aryl amide of Kemp's acid would provide a faster rate of reaction compared with the alkyl amides, and also aryl amine cytotoxins exist which could be attached as an amide.
A secondary aryl amide of Kemp's acid (58) was obtained via a potassium hydroxide ring-opening reaction on a synthesised imide of Kemp's acid (43).  
 
Aliquots of the ring-opened amide (58) were added to buffered (phosphate and malonate) aqueous solutions (with ionic strength   = 1 mol L-1) and the hydrolysis reaction followed at 30.0 oC across the pH range 0.48 - 8. First order rate constants were calculated from absorbance change with time and the pH-rate profile established. Absorbance changes were shown to be consistent with amide hydrolysis with no evidence of any imide reformation as evident in other studies. The rate data were analysed. There was no evidence from rates for the two successive acid ionisations with only a single rate plateau evident from pH 2 to 5, suggesting that both di- and mono-acid species have very similar hydrolysis rates or that the second ionisation is low due to stabilisation of the mono-ionised molecule by hydrogen bonding interactions. For this reason, the rate profile could be analysed only as if it were a single ionisation in the same way that Menger and Ladika analysed their aliphatic tertiary pyrrolidyl amide in an earlier study. This analysis gave a pKa value of 6.72   0.09 and a limiting rate constant of 7.1 x 10-5 s-1. The studies revealed a three fold rate differential between pH 5.8 (faster) versus 7.3 (slower), a difference which is probably too small a selectivity for possible prodrug application.
Separately, the second order rate coefficient for the reaction of potassium hydroxide solution to open the imide was also established (k2 = 0.00067 L mol-1 s-1 at 30.0 oC,   = 1.00 mol L-1 with KCl).

year: 2009

title: Thiourea monoanion and dianion complexes of rhodium(III) and ruthenium(II)

authors: Henderson, William

subjects: Crystal structures

abstract: The versatility of deprotonated thioureas as ligands is shown by the synthesis and characterisation of a range of rhodium(III) complexes of substituted thioureas, with support from a ruthenium(II) analogue in one case. Reaction of the complexes [LMCl(μ-Cl)]2 [M=Rh, L=η5-C5Me5 (Cp*); M=Ru, L=η6-p-cymene] with Na[MeNHC(S)NCN] and excess trimethylamine base gives the dinuclear complexes [LM{SC(=NCN)NMe}]2 containing chelate-bridging thiourea dianion ligands. The Ru complex was characterised by an X-ray diffraction study. The mononuclear complexes [Cp*Rh{SC(=NCN)NMe}(PPh3)] and [Cp*Rh{SC(=NPh)NPh}(PPh3)], containing chelating thiourea dianion ligands, were prepared by analogous reactions in the presence of triphenylphosphine. Reaction of [Cp*Rh{SC(=NCN)NMe}(PPh3)] with HCl, or [Cp*RhCl(μ-Cl)]2 with 2 equiv. of PPh3 and Na[MeNHC(S)NCN] (with no added base) gave the complex [Cp*RhCl{SC(=NCN)NHMe}(PPh3)], containing a (monodentate) S-bonded thiourea monoanion ligand, which was characterised by an X-ray diffraction study. The AsPh3 and SbPh3 analogues of this complex were also prepared and characterised. Reaction of [Cp*RhCl(μ-Cl)]2 with 2 equiv. of PPh3 or SbPh3 and PhNHC(S)NHPh or various trisubstituted thioureas PhNHC(S)NR1R2, triethylamine and NaBPh4 gave a range of cationic complexes [Cp*Rh{SC(=NR1R2)NPh}(EPh3)]+ (E=P, Sb), as their tetraphenylborate salts, in which the thiourea is bonded as a monoanion through the S and the NPh group. The corresponding reaction utilising 1,6-bis(diphenylphosphino)hexane (dpph) gave the dinuclear complex [Cp*Rh{SC(=N(CH2CH2)2O)NPh}]2(μ-η2-dpph) (BPh4)2.

text: Thiourea monoanion and dianion complexes of rhodium(III) and ruthenium(II) The versatility of deprotonated thioureas as ligands is shown by the synthesis and characterisation of a range of rhodium(III) complexes of substituted thioureas, with support from a ruthenium(II) analogue in one case. Reaction of the complexes [LMCl(μ-Cl)]2 [M=Rh, L=η5-C5Me5 (Cp*); M=Ru, L=η6-p-cymene] with Na[MeNHC(S)NCN] and excess trimethylamine base gives the dinuclear complexes [LM{SC(=NCN)NMe}]2 containing chelate-bridging thiourea dianion ligands. The Ru complex was characterised by an X-ray diffraction study. The mononuclear complexes [Cp*Rh{SC(=NCN)NMe}(PPh3)] and [Cp*Rh{SC(=NPh)NPh}(PPh3)], containing chelating thiourea dianion ligands, were prepared by analogous reactions in the presence of triphenylphosphine. Reaction of [Cp*Rh{SC(=NCN)NMe}(PPh3)] with HCl, or [Cp*RhCl(μ-Cl)]2 with 2 equiv. of PPh3 and Na[MeNHC(S)NCN] (with no added base) gave the complex [Cp*RhCl{SC(=NCN)NHMe}(PPh3)], containing a (monodentate) S-bonded thiourea monoanion ligand, which was characterised by an X-ray diffraction study. The AsPh3 and SbPh3 analogues of this complex were also prepared and characterised. Reaction of [Cp*RhCl(μ-Cl)]2 with 2 equiv. of PPh3 or SbPh3 and PhNHC(S)NHPh or various trisubstituted thioureas PhNHC(S)NR1R2, triethylamine and NaBPh4 gave a range of cationic complexes [Cp*Rh{SC(=NR1R2)NPh}(EPh3)]+ (E=P, Sb), as their tetraphenylborate salts, in which the thiourea is bonded as a monoanion through the S and the NPh group. The corresponding reaction utilising 1,6-bis(diphenylphosphino)hexane (dpph) gave the dinuclear complex [Cp*Rh{SC(=N(CH2CH2)2O)NPh}]2(μ-η2-dpph) (BPh4)2.

year: 2002-10-01

title: The Hospital Transfers Project: Supporting whanau engagement during hospitalisations

authors: Masters-Awatere, Bridgette

abstract: For Māori, as the Indigenous peoples of Aotearoa New Zealand, the care of those who are unwell has always been the concern of whānau (family) and community. Māori have established knowledge systems relating to health and wellbeing, and long-standing practices for both promoting good health and responding to illness (Taskforce on Whānau Centred Initiatives [hereafter referred to as the Taskforce], 2009; Waitangi Tribunal, 2001). These systems recognise the importance of relationships between peoples and broader environments to health and wellbeing (Mark & Lyons, 2010; Taskforce, 2009), something which has been more recently acknowledged in Māori health strategy and policy by government (Ministry of Health, 2014b).

text: The Hospital Transfers Project: Supporting whanau engagement during hospitalisations For Māori, as the Indigenous peoples of Aotearoa New Zealand, the care of those who are unwell has always been the concern of whānau (family) and community. Māori have established knowledge systems relating to health and wellbeing, and long-standing practices for both promoting good health and responding to illness (Taskforce on Whānau Centred Initiatives [hereafter referred to as the Taskforce], 2009; Waitangi Tribunal, 2001). These systems recognise the importance of relationships between peoples and broader environments to health and wellbeing (Mark & Lyons, 2010; Taskforce, 2009), something which has been more recently acknowledged in Māori health strategy and policy by government (Ministry of Health, 2014b).

year: 2019