مصنوعی/ترکیبی اینالاگ
For "analog substance" you can translate as اینالاگ مادہ

There are several possibilities for analog but in the given context (in the terms of biochemistry) best word is مماثل as analog here means some compound which has been derived from the parent compound and similar مماثل but little different. مشتق and ماخد are both good suggestions also
For Synthetic مصنوعی is common word but if you want more technical word and close to the original meaning then the exact word is تالیفی.
This word is derived from تالیف which means to synthesize

You can comnine both these words to make up the complete term
تالیفی مماثل
تالیفی مشتق
تالیفی ماخد

مصنوعی مماثل
مصنوعی مشتق
مصنوعی ماخذ

Analog here is in the meaning of a chemical isotop which is similar to the original compound but differs slightly in its chemical composition (کیمیا ؑی ترکیب)
Analog is a kind of subtype and is secondary to the original compound. so کیمیا ؑی ہمزاد is not the original compound but a subtype of secondary value.

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Note added at 3 hrs (2014-03-15 14:23:09 GMT)
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Analog is not exact replica/ copy of the original compound but differs slightly ( as in the replacement one atom of a different element), so its translation must include the word "کیمیا ؑیـی" in it.

تک بندی