A method for synthesizing PQQ, comprising the steps of: reacting a compound of Formula I where R 1 and R 4 are each independently an atom or group selected from hydrogen, a linear or branched C1-8 alkyl group, a deuterated linear or branched C1-8 alkyl group, an aralkyl group, or a substituted aryl group but not both R 1 and R 4 are hydrogen; R 2 is independently an atom or group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group; and R 3 is independently an atom or group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group, with a base or a protonic acid to obtain a compound of formula VI; where in Formula VI, OR is a group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group, reacting the compound of Formula VI with a protonic acid to obtain reduced PQQ, that is, PQP; and oxidizing PQP with an oxidizing agent to obtain PQQ or (I) reacting a compound of Formula VIA wherein R 2 , R 3 = methoxy or ethoxy with a protonic acid to obtain reduced PQQ, that is, PQP; and (II) oxidizing PQP with an oxidizing agent to obtain PQQ. reacting a compound of Formula I where R 1 and R 4 are each independently an atom or group selected from hydrogen, a linear or branched C1-8 alkyl group, a deuterated linear or branched C1-8 alkyl group, an aralkyl group, or a substituted aryl group but not both R 1 and R 4 are hydrogen; R 2 is independently an atom or group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group; and R 3 is independently an atom or group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group, with a base or a protonic acid to obtain a compound of formula VI; where in Formula VI, OR is a group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group, where R 1 and R 4 are each independently an atom or group selected from hydrogen, a linear or branched C1-8 alkyl group, a deuterated linear or branched C1-8 alkyl group, an aralkyl group, or a substituted aryl group but not both R 1 and R 4 are hydrogen; R 2 is independently an atom or group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group; and R 3 is independently an atom or group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group, with a base or a protonic acid to obtain a compound of formula VI; where in Formula VI, OR is a group selected from a linear or branched C1-8 alkoxy group, or a deuterated linear or branched C1-8 alkoxy group, reacting the compound of Formula VI with a protonic acid to obtain reduced PQQ, that is, PQP; and oxidizing PQP with an oxidizing agent to obtain PQQ or (I) reacting a compound of Formula VIA wherein R 2 , R 3 = methoxy or ethoxy with a protonic acid to obtain reduced PQQ, that is, PQP; and (II) oxidizing PQP with an oxidizing agent to obtain PQQ. (I) reacting a compound of Formula VIA wherein R 2 , R 3 = methoxy or ethoxy with a protonic acid to obtain reduced PQQ, that is, PQP; and (II) oxidizing PQP with an oxidizing agent to obtain PQQ. <EOS>