Abstract: A digital to analog converter (DAC) includes an amplifier including a buffer of the DAC, and a resistor ladder arrangement coupled to a non-inverting input terminal of the amplifier to generate a voltage based on a digital control word. The arrangement includes a first, least-significant bit, segment arranged in one of an R-2R or unit-R configuration, a second, most-significant bit, segment including one or more units each including a second-segment-resistor having a resistor terminal coupled to a respective second switch and having a second resistance, RMSB, and a third segment including one or more third-segment-resistors coupled in parallel to the non-inverting input terminal and connected to a first reference voltage terminal. M2 designates a number of bits in the digital control word for controlling the second switches, and the third segment has a total resistance, Rsp, based on M2.

Abstract: The present invention discloses a transaminase mutant and application thereof in preparation of sitagliptin intermediates, the transaminase mutant is obtained by substitution of tyrosine with proline at position 74, substitution of glutamic acid with aspartic acid at position 228, substitution of leucine with alanine at position 254 and substitution of methionine with threonine at position 290 of the amino acid sequence shown in SEQ ID NO: 2. The present invention uses wet cells or a purified transaminase as a biocatalyst and a sitagliptin precursor ketone or a prochiral carbonyl compound as a substrate to prepare a sitagliptin intermediate or a sitagliptin ester intermediate; the total yield of the method reaches about 82%, and e.e. value of the product reaches 99%.

Abstract: The present invention relates to a method for synthesizing a compound of 3-(difluoromethyl)-1-methyl-1h-pyrazole-4-carboxylic acid, wherein including the steps of: (A) the diethyl ester compounds represented by the following Formula IV are reacted under the action of amine, alkali and carbonyl reagents to produce the acrylic diester compound represented by the following Formula I, wherein: (B) the above compound represented by the Formula I is reacted with a fluoride reagent, a Lewis acid and a methyl hydrazine to form a pyrazole ring-containing diester compound represented by the Formula II, (C) the heterocyclic-containing diester compound represented by the Formula II is reacted with a base to give 3-(difluoromethyl)-1-methyl-1h-pyrazole-4-carboxylic acid represented by the Formula III.

Abstract: Provided are a preparation method for synthesizing a pyrazolecarboxylic acid derivative of the following formula (I), which is suitable for industrial production, and an intermediate as shown by the following formula (II). The method is high in reaction yield in each step, low in waste gas and waste water and low in cost, and requires no special reaction equipment.

Abstract: The present invention relates to a method for synthesizing a compound of 3-(difluoromethyl)-1-methyl-1h-pyrazole-4-carboxylic acid, wherein including the steps of: (A) the diethyl ester compounds represented by the following Formula IV are reacted under the action of amine, alkali and carbonyl reagents to produce the acrylic diester compound represented by the following Formula I, wherein (B) the above compound represented by the Formula I is reacted with a fluoride reagent, a Lewis acid and a methyl hydrazine to form a pyrazole ring-containing diester compound represented by the Formula II, (C) the heterocyclic-containing diester compound represented by the Formula II is reacted with a base to give 3-(difluoromethyl)-1-methyl-1h-pyrazole-4-carboxylic acid represented by the Formula III.

Abstract: Provided are a preparation method for synthesizing a pyrazolecarboxylic acid derivative of the following formula (I), which is suitable for industrial production, and an intermediate as shown by the following formula (II). The method is high in reaction yield in each step, low in waste gas and waste water and low in cost, and requires no special reaction equipment.